Canada’s envoy to the United States says the cross-border Nexus trusted-traveller program is being “held hostage” by a U.S. effort to renegotiate the 20-year-old agreement.

Kirsten Hillman made the comments at a daylong summit on Canada-U.S. border issues taking place at the Canadian Embassy in Washington, D.C.

The 13 enrolment centres in Canada, jointly staffed by Canadian and U.S. officers, remain closed amid a dispute over legal protections for the U.S. preclearance officers who work there.

Hillman says as the dispute drags on, the backlog of applications — more than 350,000 — only grows, while pressure to fix it continues to mount.

She says the U.S. is trying to renegotiate the terms of the agreement unilaterally, a situation she calls “disappointing” and “frustrating.”

The U.S. wants Customs and Border Protection officers at the Canadian centres to have the same legal protections they have at land border crossings and airports.

“There’s an attempt to renegotiate the terms of a 20-year-old program unilaterally, and the program is being held hostage to that effort,” Hillman said.

“There needs to be a recognition that we will work on the challenges, but we can’t have the whole program sort of on its knees until we work those through, because it’s going to take some time.”

Public Safety Minister Marco Mendicino has said U.S. customs officers at the Nexus centres aren’t entitled to the same legal protection they have at airports and the border.