President Joe Biden will no longer address the nation’s largest teachers unions this weekend after its administrative employees walked off the job Friday.

The National Education Association Staff Organization, which represents staff that works in NEA’s headquarters, said it established a picket line around the Pennsylvania Convention Center in Philadelphia, where the union’s 103rd Representative Assembly is being held. This is the group’s second strike of the year, citing unfair labor practices.

Biden was slated to speak at the convention on Sunday, the last day of the gathering, but pulled out because of the strike.

“President Biden is a fierce supporter of unions and he won’t cross a picket line,” said Lauren Hitt, a Biden campaign spokesperson, in a statement. “The President is still planning to travel to Pennsylvania this weekend, and we will have more details to share at a later point.”

The strike is expected to last through the weekend, which one union official said essentially brings the NEA convention to an early close, putting off other business and planned events.

“NEA values our staff and we remain fully committed to a fair bargaining process,” an NEA spokesperson said in a statement. “It is deeply concerning that misinformation has been shared related to our contract negotiations. This not only misrepresents the facts but also undermines the integrity of our ongoing efforts to honor a fair bargaining process.”

Key context: Last month, employees represented by the NEASO went on strike for the first time in more than 50 years.

The union has filed two unfair labor practice complaints with the National Labor Relations Board accusing NEA of “wage theft and failure to provide information requested by the staff union on outsourcing more than $50 million to contractors.” Another complaint alleges “retaliatory actions by an NEA manager against a NEASO staff member for reporting a physical assault as well as a failure by NEA to bargain over unilateral changes in working conditions.”

NEA had previously “threatened to host its convention virtually to avoid a physical picket line,” NEASO President Robin McLean said in a statement.

“It also confirms what we have been saying: NEA has abandoned its union values with its actions at the bargaining table,” McLean said. “NEA would rather cancel a multi-million-dollar convention than comply with labor law.”

Members of the union voted to authorize a strike in April amid bargaining over a new, potential three-year contract. The previous contact expired at the end of May, leaving the NEA and NEASO locked in heated contract talks. NEASO is still negotiating with NEA management over a new three-year contract. But NEASO has accused managers of the 3 million-member labor giant of using an “anti-worker playbook” at the bargaining table, including dragging out negotiations.

“Until a successor agreement is reached, there will be no labor peace,” McLean said.

Juan Perez Jr. contributed to this report.