Canada Post employees who were forced to cut their shifts short due to a bomb scare earlier this month are being penalized for their troubles, the Canadian Union of Postal Workers says.

A homemade bomb, hidden inside a grey voice recorder, made its way through the mail on July 3 before it blew up at the Petersen King law offices, seriously injuring Winnipeg lawyer Maria Mitousis. Two other explosives were also mailed, intercepted and safely detonated by the police bomb unit.

"Postal workers, under the federal labour code, have the right to refuse work when our conditions pose immediate danger," Dave Lambert, CUPW Winnipeg's local health and safety officer, said in a statement.

"There's been a lot of stress and anxiety in Winnipeg postal workplaces lately. We have to make sure our members can take steps to protect themselves."

Todd Jarema with the CUPW said about 20 workers in Winnipeg who left their shift due to bomb fears at that time have been told they won't be compensated.

Jarema said he can't understand why Canada Post has changed its mind after first telling workers the pay would not be docked.

"I think it is a disciplinary measure," Jarema said. "I don't understand why they wouldn't pay folks."

Jarema said the union plans to file grievances. Lambert said in not paying workers in these kind of situations, Canada Post is disrespecting its employees.

"We can't have Canada Post punishing workers financially for calling out potentially deadly hazards in the workplace," Lambert said.

Canada Post was unavailable to comment.