MONTREAL — A dispute over legal protections for American customs officers has kept Nexus enrolment centres closed in Canada more than three months after they reopened south of the border – due in part to a clash over U.S. agents’ right to carry guns on Canadian soil.

The standoff has led to a massive backlog in applications for the program, which allows pre-approved travellers to cross the border more quickly.

The Canada Border Services Agency says the number of Nexus applications has ballooned from 270,000 in April to more than 341,000 at a time when travel delays are wreaking havoc on passengers’ summer plans.

Agency spokeswoman Rebecca Purdy says in an email that Canada and the U.S. remain “in discussions” about when the 13 enrolment centres will reopen for applicant interviews, as the two sides try to clarify “legal protections” for American customs officers while they are working at the jointly-staffed centres.

U.S. Customs and Border Protection confirmed the hold-up revolves around legal protections for its Nexus office staff, saying in an email “one example could include the authority to carry or have access to a firearm while on duty.”

Two senior Canadian government sources told The Canadian Press the U.S. wants its customs officers who work in Nexus centres to have the same protections guaranteed to its other pre-clearance officers on Canadian soil, with sidearms as a major sticking point in the talks.