Four members of a US House Committee have asked the Environmental Protection Agency’s (EPA) Office of Inspector General to investigate the agency’s use of a study that claimed glider kit trucks do not produce harmful emissions at levels greater than trucks with new engines. The congressional letter was signed by Reps. Eddie Bernice Johnson (D-Texas), Don Beyer Jr. (D-Va.), Suzanne Bonamici (D-Ore.) and Jerry McNerney (D-Calif.), members of the House’s Science, Space and Technology Committee.

The EPA cited the study last year in a proposed rule that sought to exempt glider kits from emissions standards enacted in 2016. Those regulations—part of the sweeping Phase 2 emissions standards enacted for all truck, trailer and engine manufacturers—called for glider kit makers to be capped at building just 300 trucks a year that did not comply with modern emissions regulations. Additionally, the EPA already is investigating a competing study on glider kits, which found that they do produce higher emissions of greenhouse gases.