BISMARCK, N.D. (AP) — North Dakota regulators are proposing a fine of at least $15,000 against the company building the four-state Dakota Access pipeline.

The Public Service Commission said Monday in a complaint that a subsidiary of Texas-based Energy Transfer Partners didn’t get regulators’ approval to proceed with construction after artifacts, including stone cairns, were found last month.

The company diverted construction so the artifacts weren’t disturbed, a plan that the State Historic Preservation Office concurred with. But the PSC says the company also should have gotten clearance from regulators.

Energy Transfer Partners didn’t immediately comment. It has about three weeks to respond to the PSC complaint and either agree to a fine or request a hearing.

The $3.8 billion pipeline will carry North Dakota oil through South Dakota and Iowa to Illinois.