VANCOUVER, Aug 6 (Reuters) - Delays at the Canada-U.S. border have slowed commercial crossings to a crawl, government data shows, as Canadian border staff begin work-to-rule strike action in the midst of contract negotiations with the federal government. The wait time for commercial traffic across the Pacific Highway crossing between Surrey, British Columbia, and Blaine, Washington, was up to over five hours as of Friday evening, according to government data. The Ambassador Bridge between Windsor, Ontario, and Detroit, Michigan, the busiest land crossing between the two countries, had wait times of two and a half hours. Talks between two unions representing Canadian border guards and staff - the Public Service Alliance of Canada (PSAC) and the Customs and Immigration Union (CIU) - and the federal government reached an impasse in December 2020, and the unions served the federal government on July 27 with a strike notice. read more Both sides came back to the table after the strike notice, but the unions said on Wednesday they had been unable to reach an agreement, and their members would begin working to rule as of Friday. read more The action means staff will "perform their duties to the letter of the law," a statement from the unions said. This will include not answering questions from travelers about border regulations or collecting duties and taxes. Union demands included higher pay and the ability to carry their guns in some areas such as airports. Their members have been without a contract for three years. Both the federal government and the unions confirmed that negotiations had continued through Thursday night and into Friday, but no progress was reported. The government "will not walk away," Geneviève Sicard, spokesperson for the federal government, said in a statement on Friday. Toronto Pearson Airport, Canada"s busiest airport before the pandemic, said on Twitter that travelers should expect delays due to the strike action.