Border guards and customs officials in Canada voted on Tuesday to go on strike just days before the reopening of the border with the United States, according to unions representing the personnel, after working without a contract for three years.

The unions claim that a walkout would stifle commercial traffic at the land border, as well as international mail and duty and tax collection. However, a representative for the Canada Border Services Agency (CBSA) indicated that 90% of personnel have been designated as “essential” and will continue to work if a strike occurs.

Last week, Canada announced plans to reopen its border to fully vaccinated Americans on Aug. 9, and allowing international travelers starting on Sept. 7. The border has been shut for non-essential travel for more than 16 months because of the coronavirus pandemic.

The Public Service Alliance of Canada (PSAC) and the Customs and Immigration Union (CIU) said in a joint statement that strike action could begin as soon as Aug. 6 after 8,500 members voted in favor of the action. Contract talks reached an impasse in December 2020, the unions said.

“Taking strike action is always a last resort, but we’re grappling with systemic workplace harassment issues that must be addressed,” Mark Weber, CIU national president, said.

CBSA spokesperson Judith Gadbois said officers have proven their resilience since the beginning of the pandemic by helping to prevent the spread of the virus and its variants.

“We expect that our officers will continue to fulfill their duties with the highest level of integrity and professionalism.”