Fiat Chrysler Automobiles has been on a hot streak for more than six years, reporting growth in new car sales in the United States for 75 consecutive months, a feat rarely seen in the auto industry.

But now the federal government is asking whether those numbers are too good to be true.

The Securities and Exchange Commission is investigating whether the company has been improperly inflating its monthly sales totals, and whether those reports have misled investors.

As part of the S.E.C. inquiry, agents from the Justice Department earlier this month visited the company’s headquarters in Auburn Hills, Mich., and business centers in Dallas, Los Angeles, Detroit and Orlando, Fla., to examine records and interview company officials, a person briefed on the investigation said.

In a statement on Monday, the company said that it was cooperating with the S.E.C. and confirmed that the Justice Department had also raised questions about its sales reports.