GRAND RAPIDS, Mich. — Michigan’s senators are asking the Department of Transportation to make sure oil pipelines crossing underneath the Great Lakes are classified as “offshore” so that owners would have to pay the full costs of cleaning a spill.

Sens. Gary Peters and Debbie Stabenow, both Democrats, sent U.S. Transportation Secretary Anthony Foxx a letter on Tuesday urging him to make sure underwater pipeline segments in and around the Great Lakes are classified as separate “offshore” facilities.

The senators wrote the finding has “significant consequence,” because under the Oil Pollution Act the liability for cleanup costs for owners or operators of onshore facilities are capped at $634 million.

The senators were writing about a pipeline that belongs to Enbridge that runs under the Straits of Mackinac, which connect Lake Michigan and Lake Huron.

First Published May 22, 2016, 5:35 p.m.