(Bloomberg) -- The largest union of Canadian government employees is preparing for a strike that would disrupt immigration, passport services, tax processing and government buildings.

The Public Service Alliance of Canada, representing more than 155,000 workers who voted for a strike mandate, said “little progress” has been made during negotiations on wage increases. It’s threatening to walk out on Wednesday if there’s no deal reached by Tuesday at 9 p.m. Ottawa time. 

A potential strike comes amid a slowdown in inflation in recent months, but the union is unbending in its demands to recoup purchasing power workers lost over the past two years. PSAC says it would be the largest strike against any single employer in the country’s history. 

The union is looking for a 13.5% raise over three years for Treasury Board employees, and 20.5% over three years, plus an immediate 9% adjustment, for tax workers. The union said it’s received several wage offers but none keep up with inflation. 

Annual consumer price gains slowed to 5.2% in February, and economists in a Bloomberg survey expect March data due Tuesday morning to show inflation drifting lower to 4.3%. The Bank of Canada sees the headline rate falling to 3% by midyear, but officials warn that elevated wage growth could make getting inflation back to the 2% target “more difficult.” 

In a round of negotiations over the weekend, the government said it offered a 9% wage increase over three years for those employed by the Treasury Board, calling it “a fair and competitive offer.” PSAC didn’t see it that way.

“When the federal government represses its wages for its own employees, what they’re doing is repressing wages for workers right across the country,” Chris Aylward, PSAC’s president, said at a briefing on Monday. “That’s wrong and we’re asking the government to come to the table and set that bar for all working people in this country.”

In a statement after the union’s announcement Monday, the government said it’s “disappointed” by the threat of a strike and reiterated that it “remains committed to reaching agreements at the table that are fair to employees and reasonable to taxpayers.” 

The stakes are high for Prime Minister Justin Trudeau’s government, the country’s largest employer. Any scuffle with federal unions could draw the ire of the labor-friendly New Democrat Party, which is supporting Trudeau in a minority parliament, and widespread service disruptions would be unpopular among voters.

(Updates with inflation figures and government response)

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