York University, in Toronto, canceled all classes this morning for its 50,000 undergraduates after 3,400 teaching assistants, contract faculty members, and graduate assistants went on strike.

The striking staff is responsible for half the teaching at the university, Canada’s third-largest, according to a statement issued last night by the union, rejecting the university’s latest offer.

York had offered a 9.25-percent pay raise over three years, but the union wants 11 percent over two years, tied to the cost of living, and it wants greater job security. The two-year contract is part of the union’s overall plan to coordinate university contracts in Ontario so that collective bargaining for all universities would take place together, according to interviews with union officials in The Globe and Mail, a Toronto newspaper.

Eight years ago, the TA’s and contract faculty members were on strike for 11 weeks. —Karen Birchard