The bomb threat, the second in recent days, was called in around 7:20 p.m. Monday to authorities on the U.S. side of the bridge which links Detroit with Windsor, Ont.
In a news release issued shortly after the incident, the Detroit International Bridge Company, which owns the Ambassador Bridge, said it suspected the bogus threat had "something to do" with announced job cuts at Canada Border Services Agency.
"We cannot confirm, but suspect, that this has something to do with Canada's disinvestment at the border by cutting back on customs' agents," said the statement.
Jason McMichael, vice-president of the Customs and Immigration Union, said he was outraged at the suggestion.
"Certainly they were completely baseless, completely without merit and the members that I represent who work for the Canada Border Services Agency all across the country were insulted by them," he said from Ottawa.
Canada Border Services Agency announced cuts of more than 1,100 jobs across the country in April, including about 300 jobs in the Southern Ontario.
McMichael said that the job cuts had just started rolling out and would effect CSBA employees in a wide range of positions.
Prime Minister Stephen Harper announced construction of a new $1-billion bridge between Windsor and Detroit last month, which he said would ease traffic gridlock and encourage trade.
The new bridge will be a few kilometres south of the existing Ambassador Bridge, which has become a serious bottleneck for trucks moving between the two countries.
Canada, the U.S., auto makers and other industries have argued for years that another crossing is desperately needed to end truck gridlock and provide an alternative if the existing bridge is shut down in the event of a terrorist attack.
A spokeswoman for Public Safety Minister Vic Toews said in an emailed statement on Tuesday that the CBSA is not eliminating any frontline border guards at the Detroit-Windsor Bridge.
"The Ambassador Bridge Company, for its own commercial interests, opposes plans to construct a second Windsor-Detroit crossing," Julie Carmichael, director of communications for Toews' office, said via email. "The Detroit Police are currently investigating this incident."
Last week, a similar threat was phoned-in to authorities in Windsor that triggered a four-hour closure of the Detroit Windsor Tunnel, a busy border crossing beneath the Detroit River connecting the two border cities. No explosives were found.
U.S. authorities said the call on Monday came from somewhere in Detroit. They said the bomb threat last week was made from a pay phone in Windsor.