Tequila is optional. Constitutional liquor tax rules aren’t.

Illinois wisely scrapped a proposal that could well have violated a 1988 state Supreme Court ruling.

If you are celebrating National Tequila Day with a margarita today, the Illinois alcohol tax code probably isn’t top of mind. But the state recently scrapped a proposed new alcohol tax rule that could well have violated the Illinois Constitution.

The Illinois Department of Revenue had proposed generally classifying any product with added spirits as a spirit for tax purposes, regardless of its final alcohol content.

In Illinois, spirits are taxed over six times as much per gallon as wine and 37 times as much as cider and beer.

The department gave notice July 10 that it had pulled the proposal. If it had passed, any canned cocktails with an added spirit or any product with added spirits, such as ice cream infused with bourbon or rum, would have faced the $8.55-per-gallon rate if the final product contained more than 0.5% alcohol by volume.

The problem? That’s very close to a tax standard ruled unconstitutional almost 40 years ago.

In 1986 the state revenue department ruled that products combining non-alcoholic beverages and spirits fell into the same category as “spirits” themselves. That meant a wine cooler mixing fruit juice with wine was taxed much less than the same fruit juice mixed with spirits, even if the alcohol content was the same.

The Illinois Supreme Court found in 1988 that the department’s ruling violated the state constitution’s Article IX Uniformity Clause. Virtually identical products cannot constitutionally be taxed differently just because the alcohol is produced differently. The change the department proposed this year would appear to have done just that.

Soon after the amendments were proposed, criticism emerged from tax policy analysts and alcohol industry attorneys. The Tax Foundation argued that the rule would revive a distorted tax system and did not efficiently target the harm-causing element in alcoholic beverages: the alcohol content.

The proposal also would have hit some of the most innovative parts of the alcohol industry, including spirit-based ready-to-drinks and spirit-based high seltzers, which compete with beers, wines and ciders.

The proposed rule would almost certainly have faced objection from lawmakers on the Joint Committee on Administrative Rules, which must review all new regulations initiated by state agencies.

Even so, Illinois businesses should not have to rely on outside experts and threatened litigation to catch constitutional problems in state rulemaking.

The proposed rule change could have taxed a gallon of fruit juice with just a little bourbon in it the same as a gallon of bourbon itself. Apart from the constitutional issue, it defied common sense.