Dozens of companies doing business in the Chicago area are routing their sales through small outlying municipalities with low sales tax rates, siphoning tens of millions of dollars from city and suburban taxing districts.

These companies, ranging from catalog houses and appliance retailers to oil companies and computer purveyors, shift the official point of purchase from the Chicago area to such locations as Kankakee and Channahon in order to escape the high sales-tax rates in Cook and some collar counties. One significant advantage for the companies is that they can sell products to customers at a lower tax cost, effectively reducing the purchase price and gaining an advantage over competitors.

It's a tax-reduction strategy that has gained momentum in the past decade, fostered by consultants who help companies set up and operate satellite offices, some of which are not much more than scantily equipped storefronts. To woo and retain the remote offices, towns often rebate a portion of their sales taxes to the businesses.

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Officials of towns such as Channahon say they are adhering to rules set forth in Illinois tax code, and that the remote offices provide a few jobs and extra sales tax revenue to bolster their budgets.

"It built our village hall, which is not the Taj Mahal but is very functional, and we've had some updates to our waste treatment plant and facilities," Channahon Mayor Joe Cook said. "I don't begrudge any community that's going out to grab any dollar they can. When it all comes down to it, local government tends to be very parochial."

The tactics escaped attention until fairly recently, when the economic downturn put intense pressures on Chicago-area government budgets and leaders began to feel they were being aced out of crucial revenue.

Now, several government entities are attempting to grab back the tax dollars.

Chicago Mayor Rahm Emanuel's office said late Friday that the city plans to file a lawsuit early next week against Kankakee and Channahon. "There is money that should be going to Chicago that is going to other cities," said Chris Mather, a spokeswoman for Emanuel.

The Regional Transportation Authority, which relies on sales tax for half its budget, is working with Illinois House Majority Leader Barbara Flynn Currie, D-Chicago, on legislation aimed at blocking the tax maneuver and is hoping for a resolution during the October veto session.

"This practice has to stop; every month we lose money," said Jordan Matyas, RTA's deputy executive director.

Just how much money is at stake is hard to track. Kankakee, which observers think has the largest program, reported paying companies about $125 million in sales-tax rebates between 2002 and 2010, but if those sales had taken place in higher tax venues, they easily could have generated double or triple that amount.

Meanwhile, the state's Department of Revenue is conducting audits in 26 municipalities, most in metro Chicago, that are believed to have lost tax dollars, RTA officials said. The revenue department does not comment on whether it has audits pending, a spokeswoman said.

Cook County government is researching potential lost income as well, a spokesman said.

Within the next week, as many as eight suburbs that are home to Plass Appliance & Furniture showrooms are expected to jointly send a letter to the Revenue Department, asking for a ruling on the company's routing of sales through Channahon, said Martin Bourke, village administrator for Bloomingdale, a DuPage County suburb.

The retailer stopped paying taxes to Bloomingdale in January 2008, and the village estimates it has lost nearly $100,000 in that time. Plass executives did not respond to requests for comment.

"Plass is considered a minor player in our sales tax portfolio," Bourke said, "but the problem we have is we don't know if this is happening with other vendors."

The Bloomingdale tax rate is 8.75 percent in its business districts, compared with 7.25 percent in the portion of Channahon used by many remote offices.

Municipal administrators such as Bourke have been frustrated in their attempts to size up losses to their towns because they have been unable to obtain full lists of involved companies from the cities that offer the sales-tax incentive deals, despite requests under the Freedom of Information Act.

"You can't pierce the veil to see what's going on behind the curtain," said Brad Bettenhausen, treasurer for Tinley Park, which never received sales tax from the Plass outlet that opened there in 2007.