Speaker Mike Johnson plans on Friday to join former President Donald J. Trump at his Mar-a-Lago estate in Florida to make what he called a “major announcement on election integrity.”

It was not immediately clear what the pair were planning to discuss at their joint appearance, though Mr. Trump has continued to insist falsely that he was the true winner of the 2020 election and groundlessly accuse Democrats of attempting to interfere in the 2024 contest.

Their first public event together since Mr. Johnson was elected to the top job in the House last fall comes at an awkward moment in their relationship.

The embattled speaker is facing a threat for his ouster from one of Mr. Trump’s top loyalists in Congress, Representative Marjorie Taylor Greene, a far-right Georgia Republican. And even as Mr. Johnson has worked to show enthusiastic support for Mr. Trump, the former president and presumptive Republican nominee is stoking G.O.P. divisions and undermining the speaker’s legislative agenda in Congress.

The joint billing will come two days after Mr. Trump weighed in against legislation Mr. Johnson put forward to extend an expiring warrantless surveillance law that national security officials say is crucial to fighting terrorism and gathering intelligence. Mr. Trump urged lawmakers to “kill” the law undergirding the program, and ultraconservatives in the House banded together to block it from coming to the House floor in an embarrassing defeat for Mr. Johnson.

Mr. Johnson also is agonizing over how and when to bring to the floor a bill to send a fresh infusion of American military assistance to Ukraine — a move Mr. Trump has long opposed. (Mr. Trump has said it is “stupid” for the United States to offer foreign aid to countries instead of loans.)

And the meeting comes as Ms. Greene is escalating her threats to try to oust Mr. Johnson from the speakership if he moves forward with any legislation to send more aid to Kyiv.

“I told him not to fund Ukraine,” Ms. Greene said Wednesday after an hourlong meeting with Mr. Johnson at the Capitol to discuss their disagreements. “He did not give me an answer on that. He did not give me any guarantees.” Ms. Greene said he did offer her a position in a new “kitchen cabinet” of top advisers he wants to assemble.

Mr. Johnson, who defended the former president in two Senate impeachment trials and played a leading role in trying to help him invalidate the 2020 election results, has tried to remain in lock step with Mr. Trump since his elevation to the speakership.

He officially endorsed his presidential campaign — a move his predecessor, Kevin McCarthy, resisted — and has visited him at Mar-a-Lago, in Palm Beach, at least twice. The two speak regularly on the phone. But he is also under great and intensifying pressure from President Biden, Senate leaders in both parties and many House Republicans to defy Mr. Trump and move ahead with Ukraine aid.

In February, Mr. Johnson posted on social media a photograph of him with Mr. Trump at Mar-a-Lago, writing that they had a “great meeting” and that “together, we will grow the majority and save America!”