Truck manufacturer Navistar International Corp. (NAV) is accusing the U.S. Environmental Protection Agency of allowing rival truck makers to dictate the dominant technology for reducing pollution from diesel engines.

Navistar said the agency disregarded its own regulations and rule making procedures to accommodate companies aiming to use an emissions' treatment system known as Selective Catalyst Reduction, or SCR, Navistar alleges SCR will be less effective at reducing harmful emissions than the system it plans to use on its trucks beginning next year.

"Manufacturers convinced EPA to permit them to use SCR technology, not because it was cleaner, but because it was cheaper for them to deploy," Navistar said in a federal court filing this week. "EPA has bowed to the convenience argument of SCR manufacturers ... and tilted the playing field with relaxed requirements."

The agency did not return phone calls for a response.

The allegations are Navistar's most inflammatory to date in the company's ongoing battle against SCR. Navistar is the only truck maker in North America not using SCR. Stricter standards for tailpipe pollution from diesel-powered commercial trucks take effect Jan.1, 2010.

The Warrenville, Ill.-based company in March petitioned the U.S. Court of Appeals in Washington, D.C., to review the EPA's certification of SCR. In its latest filing, Navistar wants the court to block engine maker Cummins Inc. (CMI); Daimler Trucks North America LLC, maker of Freightliner trucks; Daimler's Detroit Diesel engine division; and Volvo Group North America Inc. from filing briefs in support of the EPA's evaluation of SCR.

"Manufacturers support EPA's position because it is, literally, their position," Navistar said in the filing.

Cummins did not respond to a call for a comment. Volvo said in a statement that Navistar's claims are a "desperate attempt to mislead the court" and accused the company of misusing data from Volvo's Web site to reach a "wildly inaccurate and misguided conclusion" about SCR.

Meanwhile, a spokeswoman for Daimler said: "We strongly disagree with the brief filed by Navistar and will respond accordingly through the legal process."

In a response filed with the court Friday, the companies said excluding them from the review would deprive them of protecting vital business interests at stake in the case.

Navistar's filing said the EPA repeatedly complied with truck makers wishes in sanctioning the use of SCR, which involves filtering engine exhaust through a urea solution to reduce nitrogen oxide and other pollutants in engine exhaust.

Navistar particularly objects to a rule allowing trucks to operate for up to 1,000 miles without a functioning SCR system. Navistar claims the exemption will allow truckers to frequently run with empty urea tanks, undermining the pollution-reduction regulations.

Navistar, meanwhile, is using a treatment system that recirculates exhaust through its engines, eliminating the need for urea and other treatment hardware used in SCR.

Critics have charged Navistar's exhaust treatment technology falls short of meeting the EPA's standards and contributes to reduced fuel economy, a key issue for commercial truck owners, by impeding the flow of engine exhaust.

-By Bob Tita, Dow Jones Newswires; 312-750-4129; robert.tita@dowjones.com