More than 12,000 faculty at Ontario's 24 public colleges are on strike after negotiations between their union and the group representing management failed Sunday evening, the Ontario Public Service Employees Union says.

The move comes after OPSEU put forward what it called a "final offer" on Saturday to the College Employer Council in a bid to avert a strike before the set deadline of 12:01 a.m. Monday.

The head of the union bargaining team, J.P. Hornick, called the proposal — which called for the number of full-time faculty to match the number of faculty members on contract — a fair path to a settlement acceptable to both sides.

"Unfortunately, Council refused to agree on even the no-cost items, such as longer contracts for contract faculty and academic freedom," Hornick said in a news release Sunday evening. "This leaves us with no choice but to withdraw our services until such time as our employer is ready to negotiate seriously."

In a statement Sunday, the CEC called the strike "completely unnecessary," saying it was unfair to students. The fastest way to resolve the strike, it said, is for the union to accept the colleges' final offer or put the offer to members for a vote.

Accepting the union's demands would add more than $250 million to annual costs, the statement said, eliminating thousands of contract faculty jobs and "jeopardizing the quality of college programs."

The strike affects more than 500,000 students.

While the strike continues, here's how it's affecting classes:

George Brown College: full-time classes suspended but Continuing Education classes continue

full-time classes suspended but Continuing Education classes continue Humber and University of Guelph-Humber: full-time, continuing education, online and corporate training classes suspended

full-time, continuing education, online and corporate training classes suspended Centennial College: cancelled full-time courses but the strike will not affect co-op placements

cancelled full-time courses but the strike will not affect co-op placements Seneca College: full-time classes cancelled (attempt being made to keep part-time studies evening and weekends running)

full-time classes cancelled (attempt being made to keep part-time studies evening and weekends running) Sheridan College : all full and part-time classes cancelled

: all full and part-time classes cancelled Mohawk College: full-time programs and all apprenticeships on hold

While classes are suspended, these college campuses remain open and several services are still being offered.