A group of Senate Democrats has launched an investigation of the regulatory process for the Tax Cuts and Jobs Act and the ways in which exceptions were made for corporations as a result of fierce lobbying with the passage of the 2017 tax overhaul.

Senate Finance Committee ranking member Ron Wyden, D-Ore., along with Senators Sherrod Brown, D-Ohio, Robert P. Casey, Jr., D-Pa., Sheldon Whitehouse, D-R.I., and Catherine Cortez Masto, D-Nev., sent a letter to Treasury Secretary Steven Mnuchin and Office of Management and Budget acting director Russell Vought asking about what they called a “giveaway to multinational corporations” through the regulatory process implementing the TCJA.

“The 2017 Republican tax law slashed the federal corporate tax rate from 35 to 21 percent,” the senators wrote. “Combined with this massive, deficit-busting tax cut, the law’s international tax provisions were supposedly meant to encourage companies to invest in the United States, rather than overseas. Instead, the new rules increased complexity and created new incentives to shift American jobs offshore. As if that was not enough, it now appears that Treasury and the OMB are using the new system’s complexity as a means to give even more tax cuts to corporations through the secretive regulatory process where corporations and their armies of lobbyists exercise undue influence.”

They complained about the process behind the regulatory rollout since the Tax Cuts and Jobs Act passed at the end of 2017. “We are well aware of the numerous glitches, mistakes, and unintended consequences contained within the hastily written tax law,” they wrote. “The Treasury Department’s willingness to rewrite the law at the behest of the largest corporations and their lobbyists only serves to compound these harms.”