NEW YORK — The now two-week-old strike by unionized school bus drivers here has been found lawful by the National Labor Relations Board (NLRB), officials announced on Friday.

The strike began on Jan. 16, with Local 1181 of the Amalgamated Transit Union calling for the continuation of job protections that Mayor Michael Bloomberg contends "the city is not legally allowed to provide."

To bring down transportation costs, New York City is bidding out contracts for 1,100 school bus routes. The current contracts expire on June 30.

In a charge filed with the NLRB Brooklyn office on Jan. 16, a group of 20 bus companies alleged that the strike was unlawful because the union’s primary dispute was with the New York City Department of Education, which contracts with the bus companies for service to area schools. The National Labor Relations Act prohibits unions from striking secondary employers in order to pressure the employer with whom they have a dispute.

However, the NLRB Office of General Counsel found that the strike does not violate the National Labor Relations Act because the union has a primary labor dispute with the bus companies.

In an advice memorandum issued on Friday, the Office of General Counsel found that the bus companies, which maintained collective bargaining agreements with the union for many years before they expired in December, are primary employers in the labor dispute, along with the Department of Education.

“It is well established that more than one employer may be a primary employer” under the National Labor Relations Act, the memo said.

NLRB officials said that, accordingly, the regional office would dismiss the charge alleging an illegal secondary strike.