The U.S. Environmental Protection Agency is reportedly investigating allegations that truck engine makers have been encouraging customers to “pre-buy” engines before stricter emissions regulations kick in October 1.

The Chicago Tribune reported the investigation Tuesday, noting that it is still in an early phase. Engine markers are prohibited from encouraging pre-buying in the 1998 consent decree they signed to settle an EPA lawsuit. That same settlement pushed up the emissions deadline by two years from the original 2004 time frame.

An EPA insider told the paper that the agency started its investigation after EPA received “some reports from other manufacturers that some companies might be circumventing the consent decree by offering extraordinary incentives” or other encouragement.

Cummins, which already has an October 2001 engine certified by the EPA, and archrival Caterpillar, which is using next-generation “ACERT” technology that is not expected to be ready by the deadline, both told the paper that they have not done anything to encourage customers to prebuy engines.

Whether or not engine makers are encouraging customers to pre-buy, it is happening, at least to some extent. Truck dealers and truck makers have told Truckinginfo.com that they can’t be sure how much of a recent pickup in orders is due to pre-buying and how much is due to the uptick in the economy. Some customers, however, have said they are pre-buying, because the new engines are expected to be several thousand dollars more expensive, and fuel mileage, maintenance and durability issues have not been addressed to their satisfaction.

A Schneider National spokesman told the Tribune that Schneider is buying now, and has no engines on order for delivery after Oct. 1. He also noted that this big bulge in pre-deadline orders diminishes many of the touted environmental benefits of the new emissions regulations.