Response times from Toronto ambulance crews are "slipping" because of the month-long strike, the city says, and it will ask the Ontario Labour Relations Board to give it the authority to force some striking paramedics to return to work.

"We are asking the Labour Relations Board to change the labour relations agreement in a significant way," said Toronto Mayor David Miller.

At a late morning news conference at city hall, Miller said a recent analysis "shows response times are slipping."

The answer, according to the city, is to get more ambulances back into service.

The City of Toronto says the strike by municipal workers is affecting its ambulance service. (CBC)

Under the current collective agreement, 25 per cent of the city's paramedics are allowed to be off the job during a labour dispute. The city wants to OLRB to change that — though it is unclear how long it will be before the board can issue a ruling.

If the city gets what it wants it will have "additional ambulances at pre-strike levels" said Emergency Medical Services chief Bruce Farr.

Farr said the strike by 24,000 municipal workers has gone on for so long it is stretching the resources of EMS. The current collective agreement, which permits some union members to be off the job, "no longer meet the needs" of the city, he said.

The EMS chief said an analysis of more than 26,000 calls since the strike began on June 22 has seen seen an increase of 53 seconds in response times. "We want to act now," he said.

The city hopes to increase the number of paramedics from 225 to 300, bringing the ambulance complement back to full.

"If granted, the application would mean an increase of 22 ambulances on a weekday and 27 more ambulances on a weekend day," the chief said.

But, Farr pointed out, the city will still remain about 100 workers short in other areas.

Farr said the application to increase the staffing levels had "nothing to do" with the death of James Hearst, who died on June 25, after collapsing in the lobby of his apartment building at 40 Alexander St.

An ambulance crew was on the scene in nine minutes, but waited for more than 30 minutes before attending to the stricken man.

Farr refused to answer any questions related to Hearst's death. That incident is being investigated by the Ontario Ministry of Health.

However last week Miller said he was concerned that the incident pointed out "weaknesses in the system — well beyond the stresses brought about by a strike."

Mark Ferguson, president of CUPE Local 416 which represents many of the striking workers, said that at this point in time there are "sufficient resources on the road to protect the health and safety of the citizens of Toronto."

Ferguson said he couldn't comment specifically on Farr's analysis on response times because he had not yet seen his statistics.