A Republican senator who met with President Trump said Thursday that Trump made it "very clear" he would not sign immigration legislation unless it starts the process of funding a wall on the southwestern U.S. border.

“In his statement today, he made it very clear that there could be something we get out of Congress that he would not sign,” Rep. Thom Tillis, R-N.C., said after he returned to the Senate from a GOP meeting with Trump. “There are certainly things that have to be negotiated in that make him feel he is fulfilling the promise he made to the American people.”

The president, who campaigned on improving border security and augmenting the wall along the Mexican border, wants the deal to include authorization for at least $1.6 billion, and possibly more, to pay for part of the border wall system, Tillis said.

“It’s laying down the authorization and other kinds of things to make sure authorizations are done, and then funding can follow,” Tillis said, describing what Republicans will insist on.

Republicans will outline their must-have immigration provisions to Democrats next Tuesday.

Bipartisan negotiations began late last year on a deal to let 700,000 young people who arrived in the U.S. illegally as children stay and work in the country, as they can now under former President Barack Obama’s Deferred Action for Childhood Arrivals program, or DACA.

Republicans want the deal to include significant border security provisions, including the authorization to fund a southern border wall system, as well as changes to the nation’s chain migration laws.

Tillis said Republicans are also discussing modifications to the visa lottery system that has been the subject of criticism because it has admitted people who later committed terrorist acts.

“We’ve reached the point now where we’ve identified all of the kinds of terms that we need to negotiate,” Tillis said. “And the president made it very clear today in a very strong way that the White House needs to be at the table and it’s the White House that is going to provide us with the leadership.”

Trump, Tillis said, “has given us broad latitude” to work out a deal with Democrats.

A bill could be ready in January, Tillis said, but it is unlikely to be included in fiscal 2018 spending bill that needs to clear Congress by January 19.