A federal grand jury has issued a subpoena for documents relating to D.C. Council member Jack Evans and legislation he promoted in 2016 that would have benefited a digital sign company, Digi Outdoor Media.

The subpoena, obtained by The Washington Post through a Freedom of Information Act request, provides the first public confirmation that the city’s longest-serving council member has been under the scrutiny of federal law enforcement officials.

The subpoena was issued to the D.C. Office of the City Administrator in late September at the request of Assistant U.S. Attorney J.P. Cooney, who heads the fraud and public corruption section of the U.S. attorney’s office for the District. A spokesman for Cooney declined to comment.

Evans (D-Ward 2) did not return messages. An attorney representing him, Mark H. Tuohey, also did not return a message Thursday. Tuohey told The Post last month that “under no circumstances whatsoever did Jack violate any law or regulation” and that “all these matters will be resolved pretty quickly.”

Federal prosecutors frequently use the subpoena power of grand juries to aid investigations. A grand jury can call witnesses, ask questions and demand records. Ultimately, if prosecutors decide to go forward with a case, it is up to the grand jury whether to indict.

In May, The Post reported that Evans created a firm called NSE Consulting in July 2016, three weeks before it received checks totaling $50,000 from Digi Outdoor’s president, Donald E. MacCord, who had launched a multimillion-dollar effort to construct digital signs across the District.

Evans said he subsequently returned the payments — which he characterized as a retainer for future consulting work — because he perceived a potential conflict of interest. Digi Outdoor had become involved with a building-code dispute with District officials, who said the signs the company was trying to erect were illegal.

In December, The Post reported that two months after Evans said he returned the payments, he received 200,000 shares in Digi Outdoor stock, which Evans also said he returned to MacCord.

A month after Evans received the shares, he asked the D.C. Council’s chairman to place emergency legislation on the next agenda that would have permitted Digi Outdoor’s signs and torpedoed city legal action against the company, while heading off any competitors that tried to follow. Evans withdrew the proposal when it became clear he lacked the votes.

The subpoena sought information about Evans’s proposed legislation and about a late-2015 legislative proposal from then-council member Vincent B. ­Orange (D-At Large) to establish clearer limits regarding signs. Orange’s proposal came at the behest of a competing sign company based in Evans’s ward that wanted to thwart Digi Outdoor’s plans. The Post has reported that Evans monitored Orange’s legislation, which never came to a vote, months before he entered the financial arrangement with Digi Outdoor.

The subpoena also sought information about legislation to allow digital billboards in and around Nationals Park, a measure promoted by a lobbyist close to Evans. The lobbyist, William Jarvis, helped Evans set up NSE Consulting and was listed as its registered agent. Jarvis has said he had nothing to do with NSE and merely helped Evans with the paperwork because they are friends. Evans’s formation of NSE was first reported by District Dig.

The D.C. Board of Ethics and Government Accountability opened an investigation early last year into Evans’s conduct. It suspended its inquiry “because of an ongoing law enforcement investigation,” its director, Brent Wolfingbarger, said at a board meeting last month.

Evans’s colleagues on the council have offered little reaction to the inquiry. Council member David Grosso (I-At Large) has voiced the most forceful criticism of Evans, calling in December for the creation of a special committee to investigate.