Picket lines have gone up and Toronto's public libraries are closed after a breakdown in negotiations between the city and the union representing library workers.

Marathon talks ended on Sunday — after four separate deadline extensions failed to produce a settlement.

Maureen O’Reilly, president of Local 4948, the Toronto Library Workers Union said that "despite our best attempts … negotiations have stalled," O'Reilly said. "We find that we are left with little choice but to take job action."

It means that the city's 98 library branches will be closed until a new deal is reached.

O'Reilly said job security is the main sticking point.

In an interview on CBC's Metro Morning, O'Reilly said the city's offer would be hard for the library workers to accept.

"Our members are already struggling to get enough hours together to make a living … and now on top of it they're facing a further threat of layoffs."

"We cannot bring back to our membership an agreement to be ratified that would allow over 50 per cent of them to be laid off, in case in 2013 if the city wants to close libraries," she said.

Toronto Public Library board chairman Coun. Paul Ainslie called O'Reilly's comments "fear mongering."

"We've never laid off a librarian. We have no intention of laying off a librarian," Ainslie said.

"I'd like to see them back at the bargaining table," he said.

Striking library workers demonstrate outside City Hall. (Patrick Morrell/CBC)

But the union doesn't appear eager to resume bargaining.

It has set up pickets at some branches and in front of City Hall on Monday, hundreds of members marched in a large circle. Among them was part-time worker Sri Pathmanathan, who agreed that job security was the key issue for her and other part-timers.

"I think we deserve to be permanent; we deserve that job security," she said.

The library is asking borrowers not to try to return books and materials for the duration of the strike, adding that no overdue fines will be charged.

CUPE Local 4948 represents more than 2,300 TPL workers. About half of those workers are part-time and about three-quarters are women.

The workers accuse the board of making unfair and impractical promises to the city this year regarding budget cuts.

Inside workers hold strike vote

A showdown is also looming between the city and its inside workers.

The 23,000 members of CUPE Local 79 are set to take a strike vote on Tuesday and will be in a legal strike position as of March 24.

Inside workers include daycare and social service workers, as well as clerks, planners and cleaners.

The inside workers' union, CUPE Local 79, has accused the city of bargaining in bad faith and filed a complaint with the Ontario Labour Relations Board.

Last month, the city's outside workers ratified a four-year agreement that included wage increases but clawed back job security.