A regulatory panel in Michigan has requested more information on a Great Lakes oil tunnel plan.

Thursday, the state’s Public Service Commission voted unanimously to seek further information about the potential for electrical fires, explosions, and other risks that could arise from the construction of a tunnel.

Enbridge Energy is seeking to extend an oil pipeline through a tunnel beneath the waterway where Lakes Michigan and Huron meet. The nearly 70 year-old Line 5 underground pipeline carries Canadian oil and natural gas between Wisconsin, Michigan, and Ontario.

Enbridge wants to replace two existing pipes in the straits with one that would run through the proposed underground tunnel. Legal battles have plagued their efforts.