Workers for the Canadian Union of Postal Workers (CUPW), for both Urban and RSMC (Rural and Suburban Mail Carriers) bargaining units issued the notice on Monday.

The rating agency changed its outlook on the U.S. to 'stable' from 'negative,' but said the government has 'failed to agree on measures to reverse the trend' of high deficits.

Finance Minister François-Philippe Champagne said the government's first priority will be to pass what the Liberals are calling a "middle-class tax cut" by July 1.