Joe Biden and Donald Trump will speak to striking auto workers in rare back-to-back events in Michigan this week, highlighting the importance of union support in the 2024 presidential election, even though unions represent a tiny fraction of U.S. workers.

Biden will join striking United Auto Workers (UAW) members on a picket line in Wayne County, Michigan, at 12:45 p.m. EDT (1645 GMT) on Tuesday, the first time a sitting president has joined a picket line in modern U.S. history. The White House did not share the exact location beforehand, citing “security concerns.”

Republican rival Trump, the front-runner to be his party’s 2024 presidential candidate, will address hundreds of workers at a gathering at an auto supplier in a Detroit suburb on Wednesday. The supplier, Drake Enterprises, is a nonunion manufacturer, according to a spokesman at the AFL-CIO. The company did not immediately respond to a request for comment.

Republicans believe Biden’s push to electrify America’s vehicle fleet, by pumping billions of dollars of tax rebates into EV manufacturing, is unpopular with auto workers.

In a statement on Tuesday, Trump accused Biden of “stabbing” autoworkers in the back. Biden’s EV mandate, he said, will “annihilate” the U.S. auto industry and cost “thousands of autoworkers their jobs.”

Biden said on Monday that the UAW gave up “an incredible amount” when the auto industry was struggling and the union “saved the automobile industry,” an apparent reference to a 2009 government bailout that included wage cuts.

“Now that the industry is roaring back they should participate in the benefits,” he said.

UAW President Shawn Fain will join Biden at the picket line and the union on Tuesday encouraged non-UAW workers to join local picket lines in support of the “historic” presidential visit. The union is not involved with Trump’s visit and Fain does not plan to attend that event, a source added.

To date, the UAW has declined to support either 2024 presidential candidate, making it the only major union not to back Biden. Both candidates are expected to sharpen their 2024 campaign message in Michigan.

“We are a long way from the general election, but it sure feels like the general election,” said Dave Urban, a Republican strategist who previously worked for Trump.

UAW workers this month began targeted strikes against General Motors (GM.N), Ford (F.N) and Chrysler parent Stellantis (STLAM.MI) seeking wage rises to match CEO pay jumps, shorter work weeks and job security as the industry moves toward electric vehicles.

The White House is holding discussions about ways to blunt any economic fallout from a full walkout.

Only 10.1% of U.S. workers were union members in 2022, but they have outsized political influence because the states where they are strong often swing from voting Democratic to Republican, and their grassroots networks are powerful influences on the working-class vote.