WASHINGTON — The Biden administration is finalizing details of a new executive action that would let the president temporarily shut the southern border to migrants if necessary, and it is in talks with Mexican leaders to get their crucial buy-in before proceeding, according to multiple officials familiar with the negotiations.

President Joe Biden directed top aides to develop plans to stem illegal migration months ago, and they are eyeing a presidential authority in the U.S. Code known as Section 212 (f), which would let the president unilaterally “suspend the entry” of specific groups of migrants whenever the number of attempted border crossings grew too great.

The administration hopes to unveil that and other executive actions in June, and it has been working with Mexico to get its cooperation on some key provisions, according to multiple officials familiar with the negotiations. No final decisions have been made, and the timing could shift.

A critical consideration is the coming presidential election in Mexico. On June 2 Mexican voters will choose a new president to serve a single six-year term.

Polls show a consistent lead for the left-leaning Claudia Sheinbaum, whose candidacy is supported by the outgoing administration of Andrés Manuel López Obrador.

Immigration is a sensitive political issue in Mexico, and there is concern major changes could affect the outcome of the election. Any new policies would most likely be made public after June 2, the officials said.

Besides invoking 212 (f), officials said, the White House is weighing a series of other steps that could be rolled out over several weeks, including at least one action that would further limit who can seek asylum at the border. 

The close coordination with Mexico underlines how essential it has become in any conversations about dealing with illegal immigration across the southern U.S. border. NBC News has reported that Mexico has nearly tripled the number of migrants it has stopped at its own southern border or inside its borders in the past year, which has driven down the number of migrants who then try to cross into the U.S.

Biden spoke with López Obrador most recently on April 28, when the two agreed to work together on migration issues.

The April conversation was seen as an inflection point in the discussions, the sources said. 

The flurry of diplomatic activity that followed has included a back-and-forth about Mexico’s role. The groundwork is being laid so Sheinbaum can work with the Biden administration to help implement the forthcoming executive actions, including the possible shutdown of the southern U.S. border, said two officials with knowledge of the negotiations.

For Biden to use his authority under 212 (f) to shut down the border when daily crossing numbers reach certain designated thresholds, Mexico would have to be willing to take back a certain number of the migrants barred from entering the U.S., two officials said.

But Mexico is already spread thin. According to officials involved in the discussions, Mexico’s enhanced interdictions and displacement of migrants have been costly. Asking Mexico to take back still more migrants would add an extra burden.

The Biden administration is preparing for legal challenges to any other executive actions it might take on immigration, including invoking 212 (f).

“I expect that if the president were to take executive action, and whatever that executive action that might entail, it will be challenged in the court,” Homeland Security Secretary Alejandro Mayorkas told reporters Monday. 

Senior administration officials have echoed that concern, with one stressing Wednesday, “We recognize that there are limits to what any administration can do in this space with executive action.”

Meanwhile, Senate Democrats are forcing a vote Thursday on the bipartisan border package that Republicans blocked earlier this year.

“Democrats are doing this because we believe in fixing the border and we have the most — the only real bipartisan bill negotiated by both sides with a real chance of passing and being put on the president’s desk,” Majority Leader Chuck Schumer, D-N.Y., told reporters Tuesday. “Everything the Republicans do has no chance of passing,” he said, referring to the House Republican border security bill known as H.R. 2.

Senate conservatives slammed the effort as “not a border security bill” at a news conference Wednesday.

“This is an election-year political stunt designed to give our Democratic colleagues the appearance of doing something about the problem without doing anything at all,” said Sen. Marsha Blackburn, R-Tenn.

Pressed by NBC News about the administration’s plans to use executive authority at the border, Blackburn said the White House is trying to “nuance this situation so that they can say, ‘We are shutting down the border.’ What we know is that they have no intention of doing that.”

“H.R. 2 would secure the border, but Schumer and [Senate Democratic Whip Dick] Durbin [D-Ill.] don’t have the spine to bring that bill forward and actually discuss border security,” she said. “So now it’s a half-measure; it’s squishes.”

The administration has stressed that the measures in the bipartisan border bill would be far more effective than executive action alone, especially when it comes to personnel and funding.

“It’s now up to Republicans in Congress,” White House press secretary Karine Jean-Pierre told reporters Wednesday. “Do you actually want to do something to solve the problem or would you rather use it as a political issue?”