A cement company with a plant in Midlothian is suing Dallas and other North Texas cities to stop them from steering their purchases to the least-polluting cement makers.

Ash Grove Texas LP, a part of Kansas-based Ash Grove Cement, contends that "green cement" resolutions violate the company's constitutional rights, as well as Texas laws on competitive bidding for public contracts.

The company sued Wednesday in U.S. District Court in Dallas.

The suit names Dallas, Plano, Arlington and Fort Worth, as well as Dallas and Tarrant counties and Dallas County Schools, which provides buses and other services to local school districts.

The suit says Dallas' adoption of a green cement resolution May 23, 2007, led the others to do the same.

The Dallas city attorney's office had no comment on the suit Monday evening.

"We have received the lawsuit today, and we are still reviewing it," said Dallas' first assistant city attorney, Chris Bowers.

The cities' environmental standards favor cement companies that use dry process kilns, which emit less smog-causing pollution than old-style, wet process kilns.

Alone among the three cement plants in Midlothian, Ash Grove has only wet process kilns.

Dallas-based TXI has four wet process kilns and one dry process kiln but idled the wet kilns indefinitely. Swiss firm Holcim has two dry process kilns.

In a prepared statement, Ash Grove attorney Marshall J. Doke said that while Ash Grove has made strides in reducing emissions, the cities illegally impose unfair conditions on cement purchases.

"In a rush to pass the cement purchasing resolutions under a slogan of 'cleaner air,' the cities of Dallas, Fort Worth, Arlington and Plano led the charge in ignoring public contracting rules and essentially imposing an emission limit applicable in other counties in their purchasing policies," Mr. Doke said.

"Ash Grove is alleging that the defendants ignored state and federal law by taking actions that stifled competition. This is not a case about air quality."

A spokesman for the North Texas environmental group that led the campaign for the cement resolutions called the suit an attempt to keep other cities from adopting similar measures.

Among them is Denton, which is scheduled to consider a green cement resolution today

"Rather than investing in a modern plant that would significantly reduce pollution, Ash Grove is investing in lawyers and suing those customers because of their legitimate concern," Jim Schermbeck of the group Downwinders at Risk said in a prepared statement. "I don't see Ford suing these cities for replacing their Crown Victorias with Priuses."