Trump says he will impose the tariffs on Mexico under the 1977 International Emergency Economic Powers Act as soon as next week unless Mexico cracks down on the flow of migrants from Central America across the southern border.

But declaring a second national emergency, after Trump used the tool earlier this year to sidestep Congress on border funding, would pave the way for a significant fight with Senate Republicans, who have publicly and privately voiced opposition to the tariffs.

A new national emergency declaration, GOP senators say, would set up a new resolution of disapproval vote in an attempt to block the tariffs from going into effect.

"Within our own groups I think we recognize that we may very well have another vote coming up," Rounds said. Johnson added the the administration "would have to be concerned" about a resolution of disapproval vote, saying "tariffs are not real popular in the Republican conference." The Senate passed a previous resolution of disapproval earlier this year to block Trump's emergency declaration along the U.S.-Mexico border. Trump, however, vetoed the measure, and Congress didn't have the votes to override him.

Republican senators are mulling a resolution of disapproval if Trump uses a national emergency to implement the tariffs against Mexico. Several sidestepped saying on Tuesday if they thought Congress could override the president on tariffs.

Tuesday's meeting comes as Republicans have been broadly opposed to using tariffs to try to force Mexico to the negotiating table on immigration, an unrelated issue.

Trump administration officials received an earful from senators during the closed-door GOP lunch, according to senators who attended the lunch.

A GOP senator who attended the meeting said that roughly a half-dozen senators spoke during the closed-door lunch, none of whom were supportive of new tariffs against Mexico.

The senator added that administration officials were warned during the lunch that they needed to count the votes on a potential resolution of disapproval because Trump could fall short.

"I think it's fair to say … that every senator who spoke, and there were probably a half-dozen, generally had the same point of view," the senator said. "Nobody was supportive, who spoke."