Rep. Conyers wants probe into Detroit-Canada tunnel, bridge bomb threats

Conyers added that the Ambassador Bridge was "the busiest commercial border crossing in the North America," and called for DHS to thorough review the threats.

"I understand various federal agencies, including the Department of Homeland Security, have been working with the Detroit Police Department and Canadian law enforcement to investigate these incidents," Conyers wrote.

"Because of the importance of these international crossings, I ask that you work with local and Canadian authorities to conduct a thorough review of the security measures for the Detroit-Windsor Tunnel and the Ambassador Bridge, and to augment current procedures by developing additional steps to protect them from harm," he continued.