Authorities shut down one of the busiest bridge crossings between Canada and the United States on Monday evening after receiving a bomb threat, according to Dan Stamper, president of the Detroit International Bridge Company.

"We take any threat very seriously, and set in motion the security measures the bridge has had in place since 9/11, staying in constant contact with first responders," Stamper said in a statement. "We cannot confirm, but suspect, that this has something to do with Canada's disinvestment at the border by cutting back on customs' agents."

The bridge closing comes four days after a man called from a street pay phone, making a similar threat to a nearby commuter tunnel that also connects Detroit to Windsor, Ontario, in Canada, The Associated Press reported. No explosives were found and the call was determined to be a hoax, according to the Detroit Free-Press.

Monday night's bomb threat was called in around 7:20 p.m. Authorities immediately stopped traffic on the bridge.