Northern Oil and Gas has fired its CEO, Michael Reger, after federal regulators indicated they are pursuing an enforcement action against him for possibly violating securities law.

Reger, Northern’s CEO since 2007, was a major participant in an investment deal that is under federal investigation for suspected stock manipulation. That deal involves a separate company called Dakota Plains Holdings, in which Northern says it has never held any interest.

Reger was “terminated” as Northern’s CEO and ceased being a member of its board effective immediately, the Wayzata-based company said in a federal securities filing Tuesday.

“The company does not believe that Mr. Reger will be entitled to any severance payment in connection with his separation from the company,” the filing said.

In connection with the federal investigation into Dakota Plains, Reger on Aug. 11 notified Northern that he had received a “Wells notice” from the U.S. Securities and Exchange Commission. The notice said SEC staff had made a “preliminary determination to recommend that the SEC institute an enforcement action against Mr. Reger,” the securities filing said.

Reger, 40, was an initial investor in Wayzata-based Dakota Plains, a publicly traded oil and sand transportation company. He has been publicly traded Northern’s CEO since 2007, owning 7 percent of the company’s stock as of April. Northern invests in oil leases and drilling projects in North Dakota’s oil fields.

Reger was the second-largest participant in a $9 million loan package that helped launch Dakota Plains. The SEC is scrutinizing that loan, as well as stock trades made in 2012. Northern reiterated in Tuesday’s regulatory filing that it has cooperated with the SEC and the agency’s investigation into Dakota Plains stock.

Northern said it does not believe that the company — or any of its conduct — is the focus of the investigation.

Reger, who could not be reached for comment, told the Star Tribune in April that he has fully cooperated in the SEC’s investigation of Dakota Plains. He also said he didn’t trade in Dakota Plains stock when it first became a public company or ask anyone else to trade.

Northern also said Tuesday that it has hired an energy investment banking outfit, signaling the company could be put up for sale.

“In light of the challenges of operating in a lower commodity price environment, Northern’s board has been evaluating strategic alternatives to increase shareholder value,” Northern said in a press statement. “To that end, the company engaged Tudor, Pickering, Holt & Co. as its financial advisor.”

Northern has been hit hard by the oil bust, losing $109 million during its second quarter, due mostly to asset impairment charges.

With Reger out, Northern’s board appointed Thomas Stoelk, the company’s chief financial officer, as interim CEO.

Stoelk, 61, has been Northern’s CFO since 2011.

Reger, whose family was in the oil business, founded Northern with Ryan Gilbertson, Northern’s former president. Reger, Gilbertson and a third former Northern executive founded Dakota Plains in 2008. Dakota’s stock began publicly trading in March 2012.

The SEC’s investigation into Dakota Plains was made public in December. The agency is looking at Dakota’s public offering and the $9 million in loans made to the company. The promissory notes had an escalator clause that paid note holders a bonus based on Dakota Plains’ stock price during its first 20 days of trading.

The shares quickly jumped to $12, stayed at or near that price for 20 days and declined, never reaching that level again. For the $9 million in loans, the bonus was $33 million.

Like Reger, Gilbertson told the Star Tribune in April that he didn’t trade Dakota’s shares during the first 20 days, and that he also has cooperated with the federal inquiry. Dakota Plains itself has said it is not the target of any SEC investigation.

Dakota Plains filed a report with securities regulators on June 30 saying the New York Stock Exchange had suspended trading in its stock and had begun delisting proceedings. The stock is currently worth 3 cents.

Northern Oil’s stock closed Tuesday at $3.73 down 25 cents.