"According to recent reports, the EPA has already issued 25 "disproportionate hardship" waivers to large, multi-billion-dollar refinining companies reporting billions of dollars of profits since 2016. Such action would represent a clear violation of your commitments and clearly undermine the President's long-standing support of the RFS.

"These waivers fall well outside the bounds of the letter or spirit of this provision in the law, which sought to provide flexibility for the smallest of US refiners, and only in cases of genuine hardship. Worse, EPA's actions are already hurting biofuel producers and farmers across the United States at a time when farm income is at the lowest levels since 2006 and retaliatory trade measures from China threaten to deepen the crisis," the senators wrote in the letter. 

Earlier this month, Reuters reported that among the recipients of the EPA's "economic hardship" waiver was Andeavor, which reported $1.5 billion in profits in 2017.

The senators, which also included Iowa's Sen. Chuck Grassley and Sen. Joni Ernst, have asked Pruitt to provide them with, among others, a full list of refiners who received waivers in 2016, 2017 or 2018 and provide the justification for those waivers.

The full letter can be read here.