Aug 4 (Reuters) - Almost 9,000 Canadian border staff will begin "work-to-rule" strike action starting on Friday, the union announced on Wednesday, days before Canada begins allowing fully vaccinated U.S. visitors in the country for the first time in 16 months. 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. 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. "We truly hoped we wouldn"t be forced to take strike action, but we"ve exhausted every other avenue to reach a fair contract with the government," Chris Aylward, PSAC"s national president, said in a statement. Union demands include higher pay and the ability to carry their guns in areas like airports, among others. The Canada Border Services Agency said in a statement it would "respond quickly to any job action/work disruption in order to maintain the safety and security of our border." The Treasury Board of Canada, which is a party in the negotiations, said in a statement it had asked for a mediator to be appointed "to help bridge the differences," adding that "the government has never walked away from these negotiations and remains available at the bargaining table." Businesses across Canada fear a negative impact, especially given the timing, just when they were expecting the first influx of tourists since the pandemic began. Canada will allow fully vaccinated U.S. visitors into the country starting on Monday. "We are bracing ourselves that there will be a slowing of the flow at the ports of entry, which under the current circumstances is certainly not ideal, given that we"ll see volumes on the border," said Mark Agnew, vice-president of policy and international with the Canadian Chamber of Commerce. The unions have previously said that a strike would slow down passenger and commercial traffic at the land border as well as impact international mail and collection of duties and taxes.