House Speaker Nancy Pelosi (D-Calif.) is joining with Senate Majority Leader Mitch McConnell (R-Ky.) and other congressional leaders to extend a rare bipartisan invitation to NATO’s secretary general to address a joint session of Congress next month.

McConnell and Pelosi held quiet talks about the idea of an invitation to Jens Stoltenberg as they eye ways to honor NATO as it celebrates its 70th anniversary in April and underscore the U.S. commitment to the group’s values and importance in securing global order, according to three people familiar with the discussions who were not authorized to speak publicly.

“Leader McConnell and Speaker Pelosi have agreed to invite Secretary-General Jens Stoltenberg to address a joint session of Congress this spring,” McConnell’s office said Monday afternoon. “We will have additional details of the Secretary-General’s speech in the weeks to come.”

The invitation to Stoltenberg comes as President Trump’s nationalistic foreign policy has rattled U.S. allies and NATO members — and as he has pushed them to pay more for having U.S. troops stationed on their territory and framed the alliance in transactional terms.

In particular, Trump has told his aides in recent weeks that he has devised an eye-popping new formula for U.S. allies, including NATO countries, although he has not implemented it.

Under his proposal, countries would pay the full cost of stationing American troops on their territory, plus 50 percent, according to U.S. and foreign officials familiar with the idea, which could have allies contributing five times what they now provide.

Trump calls the formula “cost plus 50,” and it has struck fear in the hearts of U.S. allies who view it as extortionate.

Republicans such as Rep. Liz Cheney (Wyo.), a member of party leadership, have criticized the suggestion. “It would be absolutely devastating,” Cheney said Sunday on NBC’s “Meet the Press.”

“It’s going to be very important for us to make sure that people understand the danger that will do to our relationships and to our fundamental security,” Cheney said. “Our security, we’ve been able to protect it because of our alliances and because we have been able to work with countries. We should not look at this that we need to charge them rent for the privilege of having our forces there.”

A White House spokesman did not immediately respond to a request for comment about Stoltenberg addressing a joint session of Congress. NATO declined to say whether Stoltenberg would accept the invitation, saying that his schedule during his Washington trip in April “will be announced in due course.”

The invitation could put the NATO leader in a slightly awkward position. Stoltenberg has gone to great lengths to foster a positive relationship with Trump. If the congressional invitation were seen as too direct a rebuke to the White House, it could suck him into a domestic U.S. political battle he has been eager to avoid.

Trump is personally friendly with Stoltenberg and has praised him, making frequent comments about the former Norwegian prime minister’s efforts to increase members’ financial contributions to NATO in exchange for U.S. military operations. And even as many European leaders cringe at Trump, Stoltenberg has strained to give Trump credit for shaking up negotiations over NATO finances and the U.S. military’s support.

“After years of cutting defense budgets, they have started to add billions to their defense budgets,” Stoltenberg said last July at a meeting with Trump.

“Why was that last year?” Trump asked.

“Because of your leadership, because of your carried message,” Stoltenberg told Trump. Trump then joked that reporters “won’t write that, but that’s okay.”

McConnell has been a defender of NATO and has split with Trump over the president’s skepticism of the alliance, beginning with the candidate’s assertion during his 2016 presidential campaign that he wouldn’t automatically come to the defense of NATO allies if they were attacked.

The majority leader also aligned himself with former defense secretary Jim Mattis when he abruptly resigned in December, urging Trump to nominate a successor who shared Mattis’s support for global alliances.

McConnell had initially reached out to Pelosi with the idea to extend an invitation for Stoltenberg, according to a person familiar with the discussions who spoke on the condition of anonymity to describe private communications between the two leaders.

Not only did the majority leader want to demonstrate bipartisan congressional support for the alliance, but also give Stoltenberg a significant venue to address concerns — voiced most prominently by Trump — that some NATO members weren’t meeting their defense spending obligations, the person said.

The Democratic-controlled House, led by Pelosi, passed legislation in January affirming its support for NATO. The Senate passed a similar measure last July ahead of Trump’s trip to the annual NATO summit in Brussels.

In addition, Pelosi led a congressional delegation to Brussels in mid-February, where she and her colleagues met with NATO leaders, including Stoltenberg.

During the visit, Pelosi said she was asked repeatedly by NATO and European officials whether the United States was having second thoughts about its membership given reports that Trump repeatedly floated withdrawing from the alliance. She promised them the U.S. was not considering an exit, arguing that Trump controlled only one branch of the government and that NATO had bipartisan support.

“Over 50 members of Congress were there — House and Senate, Democrats and Republicans — reasserting our commitment to the transatlantic relationship between the U.S. and Europe, as well as our commitment to NATO to strengthen it,” Pelosi said following the trip. “People seemed very happy to see such bipartisanship, House and Senate, with a very positive message of the importance of that region to us.”

While Trump has repeatedly groused about NATO members’ financial contributions, his administration has worked to balance out those statements with overtures and reassurances from others. Trump broke with past U.S. presidents by omitting a pledge to common defense from his first address to NATO leaders in 2017.

Speaking last month in Poland, Vice President Pence highlighted the administration’s commitment to the NATO alliance and its core mission of a united front against Russia on Wednesday, with a caveat that American interests will always come first.

“The United States of America stands with Poland in the most successful mutual-defense alliance in the history of the world — an alliance that each of you serves to uphold and defend — the North Atlantic Treaty Organization,” Pence said. “Under President Trump, the United States will always put the security and prosperity of America first. But as the president has made clear — and as all of you prove every single day — ‘America First’ does not mean America alone.”

Michael Birnbaum in Brussels and Philip Rucker, Ashley Parker and Anne Gearan in Washington contributed to this report.