For as long as I can remember, it’s been my practice to report on the annual revenues of Chicago radio stations.

Around this time every year, I update readers on “Chicago radio’s cash register,” listing the annual revenues of the top 30 or so local stations and comparing their year-to-year sales figures.

It’s the best way I know of to gauge the strength of the market overall and the relative success of radio groups, stations and formats.

Over the years the accuracy of my reports has never been questioned because the figures are supplied by the stations themselves. Chicago broadcasters voluntarily provide monthly sales totals to the accounting firm of Miller Kaplan Arase, which compiles the data for its clients.

But this year, regrettably, I won’t be able to share the facts that people inside the business already have.

On Monday I received a letter from a law firm for Miller Kaplan Arase threatening to sue if I published “any parts of its reports, including any revenue figures which you may obtain, regardless of source.” According to the letter, my “wrongful dissemination of this information may have a negative impact, for which you will be held responsible.”

In case the message wasn’t clear enough, the letter concluded: “You are to cease and desist from using MKA data and reports forthwith.  Judge yourself accordingly.”

I wanted to post the entire letter here, but the company’s lawyer would not give me permission. “We chose to keep the matter between you and us and not to handle it publicly,” he wrote. “We would prefer that you not republish our cease and desist letter, though you certainly can state that you received one from MKA's counsel, if you like.”

This all came about, I’m told, because one of the Chicago radio market managers objected to my report last year, which correctly noted that his group’s revenues had declined from the previous year.  Although I obtained the figures from sources outside of Miller Kaplan Arase, the disgruntled manager pressured the accounting firm, which in turn, threatened me.

As much as I’d hoped to publish the figures this year, I don’t see how I can. Without the deep pockets of a newspaper or other news organization to back a fight, I have no recourse but to acquiesce.

Just wanted you to know.