OTTAWA -- The biggest union representing public servants in Canada is seeking damages after the federal government missed a deadline for implementing four collective agreements.

The move formalizes a complaint launched in October by the Public Service Alliance of Canada after the Liberal government openly admitted problems with its Phoenix pay system would mean it would miss a 150-day deadline to pay three years' worth of back pay and implement pay raises under the agreements.

The new contracts were ratified in June.

Failure to meet the deadline came even after PSAC gave the government an additional two months to make the changes.

In a statement released today, the union said it has asked the Federal Public Service Labour Relations Board to declare the government has violated its obligations under law.

PSAC said it was also calling on the board to order the government to provide a firm date for implementing the collective agreements, and to negotiate damages for civil servants covered by the contracts.

"If, after two months, these negotiations do not yield an agreement on damages, PSAC is asking the board to intervene," the union said in a statement on its website.

The bargaining agent didn't say how much it is seeking in damages. It's not clear how many government departments or agencies have failed to fully implement the contract changes or how many civil servants have not received back pay and pay increases.

The government had said in October that it was making implementation of the collective agreements a top priority, ahead of other Phoenix issues.

But Treasury Board President Scott Brison acknowledged the complexity of the contracts had further created slowdowns in the Phoenix pay system.

Over the past several months, Public Services and Procurement Canada, which oversees the troubled system, blamed the diversion of pay advisers to handling of contract implementation for an increasing backlog of problem pay files.

PSAC represents about 180,000 workers including federal employees in a number of departments, agencies and Crown corporations.

The labour relations board is scheduled to meet with government and union officials on Jan. 31.