Treasury Board president Tony Clement says the government wants to return to the negotiating table with Canada's largest public service union, but insists it won't budge on its effort to change the existing sick leave system.

On Monday, the Public Service Alliance of Canada walked away from bargaining meetings scheduled for this week after the government introduced proposed changes to sick leave as part of its budget implementation bill.

Bill C-59, introduced Thursday, would give the government the ability to unilaterally create a new short-term and long-term disability program if negotiations failed to produce such a plan.

The union has accused the government of acting illegally in giving Clement the power to modify the terms and conditions of the sick leave system.

Clement insists plenty to negotiate

Clement, speaking on CBC's Ottawa Morning on Tuesday, said the government will realize $900 million in savings this fiscal year from changes to the sick leave system, and said while that figure is not negotiable, negotiations are about more than sick leave.

"That 900 million is sacrosanct, but it gives me room to manoeuvre and negotiate with the unions in good faith," said Clement.

"There are lots of details, important details, that can be and should be negotiated," he said.

Clement said the government wants to replace the current system — whereby public sector employees can bank sick days — with one that instead provides them access to short-term disability benefits previously unavailable.

He said the current system does a poor job of providing for new workers who have yet to bank enough sick days.

Clement accused unions of stonewalling the government during negotiations, and said he is disappointed with PSAC's decision to walk away from the bargaining table.

While he acknowledged that he does have the power to impose a new sick leave regime, he says he hasn't done it, and wants to extend "an olive branch" to unions to return to the table.

Sick leave savings don't add up: union

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Robyn Benson, president of the Public Service Alliance of Canada, says the government's sick leave numbers don't add up. (CBC)

Speaking later on Ottawa Morning, PSAC president Robyn Benson said the government's negotiations thus far have been to present a choice that is not a choice at all: go to work sick or take a pay cut.

"How do you modernize a system when you force workers to make [that choice]?" Benson said.

Benson accused Clement of faulty logic, questioning how the government hopes to improve sick leave for two-thirds of workers and save $900 million at the same time.

"They are talking out of both sides of of their mouth," she said. "Tell us what is wrong with the system, and if there are flaws with the system, we will fix them."

Benson said the union wasn't walking away from negotiations forever, and would return to the bargaining table to deal with working conditions issues.

The Conservatives have maintained current sick leave provisions have created a huge liability on the government's books because of the amount of sick time that civil servants have accumulated over the years.

But PSAC says that the liability doesn't exist.