This does not mean the union is on strike; it means leaders can call a strike at any time if they can't reach a deal in contract negotiations with the city. It's not clear when a

Around 55,000 postal workers went on a strike Friday at 12:01 a.m. ET, according to the Canadian Union of Postal Workers (CUPW). The union says a strike came as a last resort following a year of bargaining with little progress.

Philadelphia's largest municipal employee union, District Council 33, has voted to authorize a strike against the city.

PHILADELPHIA (WPVI) -- Philadelphia's largest city workers union has wrapped up a strike authorization vote. However, ballots with the strike authorization voting will be counted on Thursday. District 33 represents at least 9,000 mostly blue-collar employees, including sanitation workers.

A union representing thousands of city employees, including sanitation workers, has voted to authorize a strike. This doesn't mean they're on strike yet but it allows union leadership to call one if necessary at any time.