Federal officials may be stepping in to try to end the school bus strike.
Bus company owners have already lodged a formal complaint with the National Labor Relations Board.
They will testify before the board on Tuesday.
The board will then make a ruling that could end the walkout.
Bus drivers and matrons with Amalgamated Transit Union Local 1181 have been walking picket lines since Wednesday to protest the city's effort to solicit new bus contracts.
The union says it wants the jobs of senior employees protected in any new contract, but the city says it can't legally guarantee those protections.
The union says it won't budge on its demand to keep that employee protection provision, known as the 'EPP.'
Some 150,000 kids have been affected by the strike, one-third of whom are special needs students.