Local Transit Union 1181 has been on strike for over two weeks.
National Labor Relations Board officials refused Friday to order an end to a two-week-old school bus strike in New York City.
Lawyers for the board issued a memorandum rejecting a complaint brought by a group of 20 private bus companies who argued the strike was illegal.
The decision mirrored past NLRB rulings and was widely expected, but will still disappoint some parents hoping for a quick end to a strike that has been hardest on students with disabilities.
Around 8,000 drivers and bus aides with Local 1181 of the Amalgamated Transit Union walked off the job Jan. 16 as part of a complicated labor dispute revolving around job security provisions.
Just a fraction of New York City's public schoolchildren ride buses, but about a third of the 150,000 who do are special education students, including children who use wheelchairs.
Replacement drivers have been brought in for some of the affected routes.
The bus companies argued in their NLRB complaint that they were essentially caught in a dispute between the union and the city.
The workers were angered when the city announced last month that it could no longer require private companies bidding for transportation contracts to hire drivers by seniority and protect previous pay rates. That, and the expiration of the union's collective bargaining agreement with a coalition of bus companies in December, prompted the walkout.
Federal law generally prohibits workers from striking against a secondary employer in order to punish a primary employer, but the NLRB said that doesn't apply in this case because both the city and the bus companies are primary employers.
The chief lawyer for the New York City School Bus Contractors Coalition, Jeffrey D. Pollack, said he intends to appeal.
"The bus companies will continue to do everything we can to get the buses rolling so we can get New York City's school children back to school safely," he added.