WASHINGTON – The U.S. Department of Labor is investigating certain investments, expenses, loans and distributions made by 3M's pension plan, the company revealed this week in a Securities and Exchange Commission filing.

The Labor Department notified 3M of the investigation in April 2015. But a Star Tribune search of annual and quarterly reports showed that the first time the company mentioned the investigation to shareholders was in its May 3, 2017, filing for the business quarter that ended March 31, 2017.

A 3M spokeswoman said that the company would have nothing to say beyond what was written in the recent quarterly report. The statement in that report reads:

"The U.S. Department of Labor (DOL) notified 3M in April 2015 that it had commenced an investigation of 3M's pension plan pursuant to the federal Employee Retirement Income Security Act of 1974, as amended (ERISA).

'The DOL has stated its investigation relates to certain private equity investments, plan expenses, securities lending, and distributions of plan benefits. In response to certain DOL requests, 3M produced documents and made employees available for interviews. In December 2016, the DOL issued certain subpoenas to 3M and 3M Investment Management Corp. relating to this investigation. 3M has produced additional responsive documents and is ­cooperating with the DOL in its investigation. The DOL has not provided a timeline for the completion of its investigation."

The government did not return a call seeking comment.

The pension plan was worth nearly $19.7 billion, according to the 2016 3M annual report.

The law allows pension funds to invest in private equities, said Joshua Gotbaum, who directed the U.S. Pension Benefit Guaranty Corp. from 2010 to 2014. Companies may also lend securities and incur reasonable expenses to manage and distribute pension funds.

According to its May 3 SEC filing, 3M has had trouble with some of its pension fund investments. In 2009, the company found out that the general partners of WG Trading, in which 3M held a limited partnership, were under criminal investigation and being pursued civilly by the SEC and the Commodities Futures Trading Commission.

From 2011 to 2013, 3M also made investments in the "natural gas fired power generation industry." One of those investments, Panda Temple Power, LLC, filed for Chapter 11 bankruptcy protection in April.

Jim Spencer • 202-662-7432