The U. S. Supreme Court recently gave its blessing to the Internal Revenue Service to guess what some employers owe in taxes. The specter of the IRS guessing at tax liability is enough to scare any red-blooded American. This IRS policy is not only frightening it is unfair.

The case actually involved taxes on tips earned by waiters and waitresses. Restaurant owners are required to pay 7.65 percent Social Security tax on their employees’ total income. Since employees don’t always report all their tips, the IRS could not be sure that restaurant owners were paying enough Social Security taxes.

So, the IRS wanted permission to guess. They got it. In a 6-3 ruling, the Supreme Court upheld a federal law that allows the IRS to estimate cash tips based on tips from credit card receipts. Attorneys for the restaurant owners had argued unsuccessfully that the IRS formula doesn’t factor in stingy cash tips, takeout meals, or tip sharing among the wait staff.

The ruling affects 200,000 restaurants and many other businesses where employees receive tips, like hair salons and taxicabs. Three Justices dissented, saying the court’s decision “saddles employers with a burden unintended by Congress.”

There’s another problem with this practice. It’s unfair.

IRS Commissioner Charles Rossotti said the court’s ruling “upholds our ability to make sure all Americans pay a fair share of taxes.” Yet the IRS doesn’t apply its formula fairly. It uses its controversial formula only on employers — not on employees.

On principle, if the tax collector is allowed to guess at tip income to calculate a restaurant’s tax bill, it should guess at the waiter’s tips to calculate income taxes. That’s equal treatment under the law.

Although the Supreme Court has ruled, the case isn’t over. The next step for restaurant owners is Capitol Hill, where lobbyists will try to convince Congress to change the law.

In the meantime, I have a tip for the IRS: If you’re going to enforce tax laws, you should do so fairly by treating everyone — employers and employees — equally.