HARRISBURG, Pa. (AP) — President Joe Biden canceled a planned speech in Philadelphia at the annual conference of the National Education Association after the union’s staff announced a strike and set up picket lines Friday.

Biden had planned to speak Sunday, but his campaign said the president is a “fierce supporter of unions and he won’t cross a picket line.” The picket line effectively ended the weeklong convention, canceling the last three days of programming, the NEA said.

The NEA, which has school employee union affiliates in every state, has endorsed Biden.

Biden, who is fighting to save his endangered reelection effort, was still planning to travel to Pennsylvania over the weekend, his campaign said.

The NEA’s union, the National Education Association Staff Organization, set up picket lines Friday around the Pennsylvania Convention Center in downtown Philadelphia and had a three-day strike planned at the event.

The NEA’s union said it has filed two unfair labor practice complains over what it says are the NEA’s failure to comply with basic union requirements.

It is accusing the NEA of unilaterally removing holiday overtime pay and failing to provide information on outsourcing $50 million in contracts, it said.

In a statement, the NEA said it remained fully committed to a fair bargaining process. It also said it was “deeply concerning that misinformation has been shared” that misrepresented contract negotiations.