U.S. Trade Representative Robert Lighthizer, charged with implementing President Donald Trump’s economic nationalist trade agenda, has come under fire from some Republican senators, according to a Tuesday report from The Hill.

Lightizer’s top priority has been Trump’s campaign promise to renegotiate the North American Free Trade Agreement (NAFTA), which has run into stiff opposition from fellow-signatories Mexico and Canada. According to The Hill, these Republican senators, including John Cornyn (R-TX), Pat Roberts (R-KS), and Orrin Hatch (R-UT), are worried Lightizer “is not listening to Congress’s feedback” on these negotiations.

“There’s a number of frustrations with their approach including … they need Congress to ratify it under [Trade Promotion Authority (TPA)] and so they don’t seem to be paying that much attention to what members of the Senate think,” Cornyn told The Hill after a recent Senate Finance Committee meeting with Lightizer.

“Members are frustrated the administration isn’t regularly consulting with them during NAFTA negotiations as they’re obligated to under TPA,” a “Senate Republican aide” added.

As The Hill notes, states like Texas and Kansas conduct a large amount of trade with Mexico, including agricultural exports. Sen. Roberts claimed:

It would be a paradox of enormous irony if here we’re passing a tax bill to achieve economic growth and on the other side of it pulling the trigger on NAFTA — if the president would do that — could very well cause a farm recession and a stock market reaction that would be very counterproductive.

Most upsetting to the pro-free-trade senators was Trump’s contention NAFTA should be renegotiated every five years. “If you do that, I don’t know that anyone would sign up,” Roberts said of the proposal.

Some Republican senators were also displeased and skeptical over the pace of bilateral trade negotiations in place of the now-abandoned Trans-Pacific Partnership. The administration had indicated it would aggressively pursue some bilateral trade deals but has encountered significant difficulty in negotiations.

For example, Sen. Ron Johnson (R-WI) told The Hill, “I’ve always said I’m happy to have another administration negotiate better trade deals but we have to negotiate the trade deals and we’ve got to get moving on it or we’re going to be left behind.”

Lighthizer, who served as Ronald Reagan’s deputy trade representative, is a long-time critic of free-trade fundamentalism in the Republican Party and has been especially critical of free-trade theory’s ability to handle a rising China. He was confirmed back in May after the president picked him as the man to implement the re-evaluation of American trade policy on which Trump ran.