DETROIT — The Ambassador Bridge was shut down for the second time in a week last night, after another bomb threat was made to police.

According to various media sources, a call was made to police stateside around 7:20 p.m. ET Monday. The caller said a bomb would go off in 10 minutes along the busy freight crossing.

Authorities set up a one-kilometre safety zone on both sides of the bridge, while police on either side of the border used boats to secure the waterway.

No incendiary devices were found during the sweep. The bridge re-opened at 1:00 a.m. ET.

While the bomb threat came on the U.S. side of the border, the phone call, police said, came from Windsor.

In a statement emailed to media sources, Detroit International Bridge Company president Dan Stamper said that while they cannot confirm, they suspect “that this has something to do with Canada’s disinvestment at the border by cutting back on customs’ agents.”

According to CBC, Jason McMichael first national vice president of the Customs and Immigration Union, said Stamper’s comments were “mindless rhetoric” and “so perverse, it’s laughable.”

“Despite the fact they are faced with cuts and despite the fact they have been working without a contract for the last year, these folks go to work every day and protect the Canadian economy, Canadians and international travellers,” McMichael said of his union’s members.

“In my mind, it is out of the realm of possibly,” he said. “What could possibly be accomplished that would — in any way, shape or form — aid my members?”

The Ambassador Bridge carries a reported 25 percent of Canada-U.S. trade. In 2010, a reported 28,814 trucks crossed the bridge daily.

For more on the story, check out the CBC here.