President Joe Biden will travel to Michigan to join the picket line of auto workers on strike nationwide, he said on Friday afternoon.

“Tuesday, I’ll go to Michigan to join the picket line and stand in solidarity with the men and women of UAW as they fight for a fair share of the value they helped create,” Biden wrote on X, the platform previously known as Twitter.

His decision to stand alongside the striking workers represents perhaps the most significant display of union solidarity ever by a sitting president.

The president’s plans come as some Democrats have begun to question his response to the strike, recognizing that he needs the full backing of union workers in his presidential reelection bid.

Earlier on Friday, United Auto Workers President Shawn Fain announced that the strike would expand to more than three dozen additional locations across the country, rapidly expanding the union’s picket line that began at just three plants last Friday. Fain also asked Biden to join the workers on the picket line.

Former President Donald Trump also has plans to visit Michigan next week. Despite backlash from Fain, the leading candidate in the Republican presidential primary will visit current and former workers next Wednesday — the same day his competitors in the field take the debate stage in California.

Holly Otterbein and Sam Stein contributed to this report.