Commercial truck drivers trying to cross the border into Canada from New York and elsewhere in the United States endured massive delays on Friday, after a labor dispute between customs workers and the Canadian government escalated.

In Buffalo, trucks attempting to use the Peace Bridge crossing waited as long as three hours, with the line of vehicles extending back into the city’s downtown areas. Delays were also extensive at crossings in Detroit and in Sumas, Washington.

Attn: freight traffic — this is quickly becoming a large and long backup. It is now blocking from the #Canadian border, down SR 543 and taking up the right lane on northbound I-5 at exit 274. https://t.co/Co4w2Mr5dq pic.twitter.com/deyQ7NmAY9

— WSDOT Traffic (@wsdot_traffic) August 6, 2021

The Public Service Alliance of Canada and its Customs and Immigration Union started a work-to-rule strike on Friday morning, meaning workers were at their jobs but strictly observing staffing and breaktime regulations.

On its website, the union posted, “Don’t work during your breaks or unpaid lunches. Don’t work past your scheduled work hours. Ask every question in your manual at ports of entry. This may cause long and unavoidable delays at Canada’s borders, but we know you take pride in your work and will rely on your discretion to not cut any corners while performing your duties.”

The strike started just days before the Aug. 9 start of fully vaccinated U.S. citizens being able to visit Canada without having to quarantine for two weeks.

The union, representing about 9,000 Canadian Border Service Agency workers, voted late last month to authorize the strike.

The employees include 5,500 border services officers, 2,000 headquarters staff and other workers at various facilities.

The union and the government agency have been in negotiations for the past few years, but have been unable to reach agreement on issues including staff protections and remote work provisions.

(AP)