The New York City schools chancellor, Dennis M. Walcott, said on Sunday that a strike by the city's school bus drivers was all but inevitable and angrily dismissed it as "irresponsible and disrespectful" to students and parents.
At a news conference at the Tweed Courthouse, Mr. Walcott, citing various news reports indicating that a walkout could occur as early as Wednesday, said it was "not now a matter of if, but when, a strike will take place." He added that union leaders had promised to inform the Education Department 24 hours before beginning the strike and had yet to do so.
Maggie McKeon, a spokeswoman for Local 1181 of the Amalgamated Transit Union, which represents 9,000 bus drivers, would not say whether union leaders had agreed to strike.
A strike could affect as many as 152,000 public and private school students who rely on yellow bus service. The city has said it would provide parents and students with MetroCards and reimburse fares paid to taxis and car services for those without access to public transportation.
Raising tensions further, three bus contractors announced Sunday that they would file charges of an unfair labor practice against the union if it stopped work, and would request an injunction against it from the National Labor Relations Board.
In a letter sent to the union and made available to reporters, a lawyer for the contractors said they would also file civil complaints seeking millions of dollars in damages that "would likely deplete union coffers."
The dispute erupted last month when the Education Department announced that it would accept competitive bids for transporting 22,500 special-needs children, who require special services. The contracts would cover 1,100 bus routes, about a sixth of the city's total.
Most galling for drivers and the union, the new contracts, among other things, would omit longstanding job security provisions requiring new companies to hire veteran bus drivers by order of seniority and at the same pay rate. The protections were put into effect in 1979 after a 13-week walkout. There have been no strikes since.
Officials, including Mr. Walcott and Mayor Michael R. Bloomberg, have argued that a 2011 ruling by the Court of Appeals, the state's highest court, prohibited the city from including the protective provisions in new contracts. The union has said the ruling applied only to contracts for busing prekindergarten students.
The ruling prompted a similar confrontation last year when the Education Department issued a request for competitive bids to transport 14,000 preschool students with special needs. In that instance, threats of a strike by the union never materialized.
On Sunday in his weekly radio address, Mr. Bloomberg said: "There's nothing the city can do to meet the union's demands. In a year when our students have already missed a week or more of school because of Hurricane Sandy, a strike would be totally irresponsible."
The mayor said last year's contracts, which were also stripped of protections, would save taxpayers $95 million over five years. He predicted further savings with the latest round of bidding, and he offered little indication that the city was willing to negotiate the point.
This article originally appeared in The New York Times.