York University will not negotiate away its right to recruit from among the world's most talented academics and to bring a diversity of views into the university's classrooms, the school's president said on the first day of a strike by part-time instructors and teaching and graduate assistants.

"Any university will want to ensure that you are looking outside because you want to bring in different academic perspectives, certainly from Canada, [and] certainly from around the world," Rhonda Lenton said.

One of the key outstanding issues in the dispute is the ability of long-time contract instructors to have their positions converted to tenure-track posts. Maintaining a pathway between temporary and permanent work is a way to protect instructors from being trapped in precarious work, the union representing the roughly 3,000 strikers said.

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"You have to have taught for at least 10 years to be eligible for the program," said Lina Nasr, the spokeswoman for the Canadian Union of Public Employees (CUPE), Local 3903. "This is about job security, this is about stable work for our members," she said.

This is the second labour dispute at York in 36 months, with members of the same union walking out in the spring of 2015. Unlike three years ago, however, the university is keeping all classes that can run open for now, hoping to minimize the impact on 46,000 undergraduates who are in the last month of classes before exams. Part-time instructors teach 39 per cent of all classes, York said. (CUPE says that when teaching assistants are counted, that percentage is 60).

York is trying to give contract instructors more security by taking other measures, such as increasing the length of long-term postings, and creating new categories of renewable appointments, Dr. Lenton said.

When it comes to tenure-track hires, however, the university must protect the right of departments to select the best candidate, she said.

"What we've been trying to say to the union is we need to prioritize student success and academic excellence, and the majority of tenure-stream faculty appointments should be achieved through [open] searches," Dr. Lenton said.

Temporary contracts have become an increasing source of labour tension in higher education around the world, including in Canada. Faculty at Ontario's 22 colleges took to the picket lines for five weeks last fall, with a key demand being an increase in job security for part-time and temporary professors. It was the province's longest strike in the college sector and a provincial roundtable is now discussing the issues that emerged.

The strike comes only halfway through Dr. Lenton's first year as president. She took over the leadership of the university this past summer, after serving as provost for five years. A search for a new provost is under way.

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Dr. Lenton said she is disappointed in the outcome of six months of labour negotiations and the rejection of an offer that contains the best wages for contract instructors and teaching assistants among Ontario universities. But she respects the union's right to strike.

"I went in [as president] understanding that York values a diversity of perspectives … and people have ideas about what is fair, what is manageable and what can be done," Dr. Lenton said.

It is not clear what will bring the two sides back to the bargaining table. Dr. Lenton said York is waiting for a counter proposal to its last offer, which was rejected on Friday. The union said it submitted a proposal, but there was no bargaining over the weekend.

"There is a lack of trust," said Ms. Nasr, of CUPE 3903. "We have not seen them take our issues seriously. These are not specific issues; these are sectorwide issues. Precarious work is a problem."