The opinion of the court was delivered by: Justice Rarick
 Docket Nos. 94127, 94128, 94171 cons.-Agenda 10-November 2003.
 Before us is a class action challenging the constitutionality of Public Act 91-38, which amended provisions of the Liquor Control Act of 1934 (235 ILCS 5/1-1 et seq. (West 2000)), the State Finance Act (30 ILCS 105/1 et seq. (West 2000)) and the School Construction Law (105 ILCS 230/5-1 et seq. (West 2000)). On cross-motions for partial summary judgment, the circuit court of Cook County held that the statute violated the three readings and the single subject clauses of article IV, section 8(d), of the Illinois Constitution of 1970 (Ill. Const. 1970, art. IV, §8(d)). It rejected the contention that the statute violated our constitution's uniformity clause (Ill. Const. 1970, art. IX, §2). Defendants appealed. Plaintiffs cross-appealed. An intervening defendant filed a separate appeal. Because the circuit court's judgment invalidated a state statute, the appeals were taken directly to our court. 134 Ill. 2d R. 302(a)). For the reasons that follow, we reverse and remand with directions to dismiss.
 Public Act 91-38, the statute challenged in this case, amended section 8-1 of the Liquor Control Act (235 ILCS 5/8-1 (West 2000)) by creating a single tax rate for manufacturers of wine and by raising the state liquor tax, which is levied on manufacturers and importing distributors of alcoholic beverages. It amended the State Finance Act (30 ILCS 105/1 et seq. (West 2000)) to authorize the expenditure of funds from the General Revenue Fund for public infrastructure improvements. In addition, it amended the School Construction Law (105 ILCS 230/5-1 et seq. (West 2000)) to authorize certain grants for school construction and maintenance projects.
 Shortly after the Public Act 91-38 took effect, an attorney named Saul Wexler brought an action in the circuit court of Cook County to challenge its constitutionality. Wexler is neither a manufacturer nor an importing distributor of alcoholic beverages, nor does he have anything to do with public infrastructure or school construction or maintenance projects. He challenged the law as a retail purchaser of Smirnoff vodka. He claimed that he bought several bottles of the vodka at Evanston First Liquors after the statutory amendment took effect. Wexler asserted that he had the right to challenge the law because the higher tax was passed along to retailers and then to consumers in the form of higher prices. As a result, he had to pay more for his Smirnoff vodka than he would have absent the tax increase.
 Wexler's complaint named as defendants Sankar, Inc., the company that owned Evanston First Liquors; the Wirtz Corporation, d/b/a Judge and Dolph, the importing distributor that supplied the vodka to Sankar, Inc.; Glen Bower, in his official capacity as Director of Revenue; Daniel Hynes, in his official capacity as Comptroller of the State of Illinois; and Judy Baar Topinka in her official capacity as State Treasurer. The circuit court granted preliminary injunctive relief to Wexler, denied the state defendants' claim that Wexler lacked standing to challenge the law, and certified a plaintiff class. Various other motions were considered and additional orders were entered. Cross-motions for summary judgment were filed by plaintiffs and defendants. Anheuser-Busch intervened as an additional defendant and filed its own motion for summary judgment.
 The circuit court ruled on the summary judgment motions in April of 2002. Wexler's challenge to the statute was successful. Although the court rejected Wexler's contention that Public Act 91-38 violated our constitution's uniformity clause (Ill. Const. 1970, art. IX, §2), it found that the statute violated the three readings rule and the single subject clauses of article IV, section 8(d), of the Illinois Constitution of 1970 (Ill. Const. 1970, art. IV, §8(d)).
 In a subsequent order, the circuit court granted permanent injunctive relief to plaintiff. It stayed the permanent injunction pending appeal, but ordered the tax owed by Judge and Dolph under the challenged law to be paid into a protest fund until the appeal was resolved. Following resolution of a motion to reconsider, the court made an express written finding under Rule 304(a) (155 Ill. 2d R. 304(a)) that there was no just reason for delaying enforcement or appeal. The matter is now before us for review.
 A threshold question on this appeal is whether the circuit court erred in rejecting the state defendants' assertion that Wexler lacked standing to challenge the statute. Under Illinois law, lack of standing is an affirmative defense. A plaintiff need not allege facts establishing that he has standing to proceed. Rather, it is the defendant's burden to plead and prove lack of standing. Chicago Teachers Union, Local 1 v. Board of Education of the City of Chicago, 189 Ill. 2d 200, 206 (2000). Where a plaintiff has no standing, the proceedings must be dismissed. That is so because lack of standing negates a plaintiff's cause of action. See Wood River Township v. Wood River Township Hospital, 331 Ill. App. 3d 599, 604 (2002).
 The state defendants challenged Wexler's standing in a motion to dismiss filed pursuant to section 2-619 of the Code of Civil Procedure (735 ILCS 5/2-619 (West 2000)). A section 2-619 motion to dismiss presents a question of law. So too does the issue of a plaintiff's standing. Our review is therefore de novo. Robinson v. Toyota Motor Credit Corp., 201 Ill. 2d 403, 411 (2002); see Kankakee County Board of Review v. Property Tax Appeal Board, 316 Ill. App. 3d 148, 151 (2000).
 The function of the doctrine of standing is to insure that issues are raised only by those parties with a real interest in the outcome of the controversy. To have standing to challenge the constitutionality of a statute, as Wexler sought to do here, one must have sustained or be in immediate danger of sustaining a direct injury as a result of enforcement of the challenged statute. The claimed injury must be (1) distinct and palpable; (2) fairly traceable to defendant's actions; and (3) substantially likely to be prevented or redressed by the grant of the requested relief. Chicago Teachers Union, Local 1, 189 Ill. 2d at 206-07.
 In the case before us, Wexler claims standing to challenge the constitutionality of Public Act 91-38 on the theory that he was injured by having to pay the higher tax imposed by the statute when he bought the bottles of vodka at Evanston First Liquors. To the extent that Wexler was actually burdened by the higher tax, however, it was a burden he shouldered willingly. Under Illinois law, a taxpayer can argue that tax payments were involuntary in only two situations: (1) if he or she lacked knowledge of the facts upon which to protest the taxes at the time they were paid or (2) the taxpayer paid the taxes under duress. Geary v. Dominick's Finer Foods, Inc., 129 Ill. 2d 389, 393 (1989). Neither of those circumstances is present here.
 In assessing whether a tax was paid under duress, Illinois law does not require a showing that the taxpayer was actually threatened by anyone. Implied duress will suffice. Geary, 129 Ill. 2d at 402-03. Such duress exists where the taxpayer's refusal to pay the tax would result in loss of reasonable access to a good or service considered essential. Geary, 129 Ill. 2d at 396-400. Goods or services deemed to be necessities have included telephone and electrical service and, for women, sanitary napkins and tampons. Geary, 129 Ill. 2d at 398-99.
 Alcoholic beverages do not fall within the category of necessary goods or services. Without commenting on the social utility of beer, wine, and spirits, we note simply that they are not essential, in any objective sense, to consumers such as Wexler. They were certainly not essential to Wexler himself. There is no indication in the pleadings or the record that Wexler had ever purchased Smirnoff vodka before or needed to do so in the future. In fact, there is nothing to suggest that Wexler ever bought or wanted to buy alcoholic beverages of any kind outside of the particular purchases mentioned in his complaint. Under such circumstances, Wexler cannot contend that he paid the tax under duress.
 There is likewise no basis for holding that he lacked knowledge of the facts upon which to protest the taxes at the time they were paid. Wexler was clearly aware of the tax increase produced by Public Act 91-38 and its effects on the price of alcoholic beverages. Despite that knowledge, and despite the fact that he had no need for the vodka, Wexler nevertheless went forward with the purchases. Based on that conduct and the course of subsequent events, it seems clear that Wexler actually bought the vodka precisely because of ...