Union president Gary Corbett said he is against cutting severance packages for public sector workers. (CBC)

Canada's second largest public service union has turned down an offer from the federal government to begin contract talks early after it found out the government would be asking for concessions on severance pay.

The Professional Institute of the Public Service of Canada (PIPSC) — made up of doctors, engineers, nurses and architects — said Tuesday it's not willing to give up severance packages for higher wages, as the federal government wants.

"Severance was the hinging point for our membership across the country because it is a huge, huge concession," union president Gary Corbett told CBC News.

Corbett said cutting severance packages would reduce job security for public service workers, something that might affect future hiring.

"The consequences are that we're not going to be able to recruit and maintain public service professionals," he said.

Canada's largest public service union, the Public Service Alliance of Canada, agreed to a tentative deal with cuts to severance in early October, a move condemned by several other federal unions.

Professor Linda Duxbury, a labour expert at Carleton University's Sprott School of Business, said the union made a good decision, especially because their jobs are in high demand.

"We're moving into a huge skills shortage," Duxbury said.

"They've got the skills the market needs. They don't have to stay in the public service, they can get other jobs. So why would they have to give up anything?"

Corbett said PIPSC is open to future discussions with the government and will go ahead with the scheduled bargaining process set to begin within the next two months.