OTTAWA, April 18 (Reuters) - A union representing some 155,000 public sector workers in Canada called for a strike starting on Wednesday after failing to reach a new wage deal with the federal government, setting up a walkout that could affect tax filings and passport services.

The Public Service Alliance of Canada (PSAC) union, which has been in collective bargaining for a new contract since 2021, had set a deadline of 9 p.m. ET (0100 GMT) on Tuesday to reach a deal.

"We are still here at the table. We will remain at the table. We will remain for as long as it takes during the strike and we will remain on strike until the government addresses our key issues at the bargaining table," Chris Aylward, national president for the Public Service Alliance of Canada, told an evening news conference.

The strike will affect federal services and could delay tax refunds since about 35,000 workers at the revenue agency would be walking out in the middle of tax filing season. Passport renewals ahead of summer travel could also be delayed.

The contract negotiations cover two main groups of employees - 120,000 workers under Canada's Treasury Board, which oversees public administration, and 35,000 revenue agency workers.

Tax agency workers initially sought a pay bump of more than 30% over three years, while the other group is seeking a 13.5% pay rise over three years. Inflation peaked at 8.1% last year.

On Sunday, the federal government offered a wage increase of 9% over three years in what it said was "a fair and competitive offer."

The strike would also affect 65% of employees at the Canadian Grain Commission, including most inspectors of outbound grain at ports, according to the commission. Canada is a major wheat and canola exporter.