More than 900 part-time professors at Concordia University started a series of rotating strikes on Monday to protest delays in contract negotiations with the school.

Part-time professors, who teach about 40 per cent of the courses at Concordia, have been without a contract for six years.

On the first day, professors from the English and cinema departments walked off the job, affecting about 10 classes.

A handful of pickets marched outside the university's engineering building Monday while the board of governors was meeting inside.

"Publicly, it's all sweetness and light from the administration. Behind closed doors, they're playing hardball with us," English professor David Leahy said.

The union says the teachers have not had a pay increase since 2003 and that they get paid less than their counterparts at the University of Montreal or other universities in Quebec.

Concordia president Michael Di Grappa said the university takes some responsibility for the delay in reaching a contract.

But, he said, administration has been busy with several other labour negotiations.

"When I took over for human resources in the fall of 2005, there were about five groups that were still without a contract. We're down to one," he said.

The two sides weren't scheduled to meet again until next week, but on Monday they agreed to meet later this week.