In a letter to the Canadian company, the state Department of Natural Resources requested documents dating back to 1953, when two 20-inch pipelines were placed across the bottom of the Straits of Mackinac.

They are part of Line 5, which carries crude oil and natural gas liquids used in propane from Superior, Wisconsin, to Sarnia, Ontario. The straits connect Lakes Huron and Michigan.

Gov. Gretchen Whitmer last June ordered a review of Enbridge’s compliance with an easement that set conditions for the company to place the pipelines on the Great Lakes bottomlands.

The Democratic governor, who has echoed environmentalists’ concerns that the pipes are unsafe and could leak, said violations of the easement could justify an order to shut down the line.

“The documents requested today from Enbridge will provide important information in the department’s continuing review” of the company’s performance, said Ed Golder, spokesman for the natural resources department.

The Canadian company, based in Calgary, Alberta, issued a statement saying it had received the information request. Spokesman Michael Barnes said the company had no comment on how it would respond.

The underwater pipeline segment “has been operating safely and reliably since it was constructed more than 60 years ago,” Enbridge said.

In the letter, natural resources director Daniel Eichinger asked Enbridge to provide all company letters, emails, reports and other materials involving any spills or leaks from Line 5.

He also requested documents involving gaps that have appeared beneath the pipelines and damage to the pipes’ outer coating, as well as curves that might have formed in the piping and strikes by ship anchors or other objects.

The pipes were dented by an anchor dropped by a tugboat in April 2018, although Enbridge said they remained intact.

For Love of Water, an environmental group, praised the state’s request for company records and urged the state to terminate the easement.

“It’s clear that Line 5’s original design in the Straits is failing, as the powerful currents scour the public bottomlands and undermine the pipelines placed there in 1953,” said Jim Olson, the group’s president.

Upper Peninsula lawmakers derided the recent letter from the DNR to Enbridge.

The following statement was released on Tuesday from Sen. Ed McBroom, R-Vulcan, and state Reps. Beau LaFave, R-Iron Mountain, and Greg Markkanen, R-Hancock:

“We find it rich that, in the latest round of delaying the tunnel, the DNR Director sent a letter to Enbridge requesting a litany of information about Line 5 that the department and administration already have. This request is a clear attempt to tie the company up in more bureaucratic minutia in order to further delay the closing of the administration’s investigation and getting to work on the tunnel as quickly as possible.

“Simply put, the DNR’s review and Governor Whitmer’s challenge has gone on long enough and we are calling on the DNR to retract the letter. We believe it is in the best interest of the state that the original compromise to keep Line 5 open and operational be honored until the replacement is opened.

“The company already agreed to move up completion by 2023; why is the state seeking to cause delays again? The tunnel is the logical solution to keeping Line 5 open, our energy supply secure, thousands of workers on the job and, importantly, to helping protect the Great Lakes.”

State Rep. Sara Cambensy, D-Marquette, issued the following statement Tuesday:

“I am unsure what the Administration’s goal is in continuing to bombard a single company with tedious information requests on issues that are already public and have been thoroughly vetted by current and past state legal teams. The courts have also upheld them.

“I’m concerned. International trade laws — especially those that protect against major energy disruptions and assure international and state energy security — are in place to protect against abrupt changes in state law. At this point, Michigan is starting to become known as a state with no certainty. There is no certainty that rural residents’ energy concerns are being addressed in pragmatic, rational ways. And Michigan businesses are concerned about whether to make major investments in our state if they require large energy loads.

“After working with the Snyder Administration for a ‘double wall or not at all solution,’ environmental groups keep moving the goal post. I’m disappointed in this onerous request that has come so late in the process. It is slowing down progress on a real solution.”