President Donald Trump is setting himself up for a fight with congressional Republicans if he seeks to expand his unilateral tariff powers or proceed with threatened duties on imports of cars and auto parts.

Trump is expected to urge Congress in his State of the Union address this month to pass new legislation that would boost his powers to break down tariff and non-tariff barriers to American exports, Bloomberg News reported Tuesday.

Sen. Chuck Grassley of Iowa, who now chairs the Finance Committee with jurisdiction over trade, told reporters Wednesday that Trump will not be allowed more power because Congress has already delegated too much authority to the executive branch.

Sen. Chuck Grassley of Iowa
Senator Chuck Grassley of Iowa

“Oh, we aren’t going to give him any greater authority, we’ve already delegated too much,” Grassley said in response to a question on the Bloomberg News report, adding that his view on tariffs “is a little bit different than the president’s.”

Sen. Pat Toomey, a Republican from Pennsylvania who also sits on the Finance Committee, responded to Bloomberg’s report, saying on Twitter that “Congress should be reasserting its constitutional responsibility on trade, not yielding even more power to the executive branch.”

For much of his presidency, Trump has had free rein on trade and faced little public push back from his own party in Congress. That could change in 2019.

Trump last year used an arcane trade law to impose duties on steel and aluminum imports from the majority of U.S. trading partners on national security grounds. He is considering using the same authority to hit car and auto parts imports with tariffs as early as next month, causing Republicans to examine if they should limit his trade authority.

“I do not believe that we should alienate our allies with tariffs disguised as national security protections. And certainly not when it comes to trade in automobiles and auto parts,” Grassley said in a statement late Wednesday.

“For this reason, I intend to review the president’s use of power under Section 232 of the Trade Act of 1962, which grants the president broad legal authority to impose tariffs in the name of national security,” he said.