The Internal Revenue Service is investigating longtime National Rifle Association CEO Wayne LaPierre for possible criminal tax fraud related to his personal taxes, according to people familiar with the matter.

Mr. LaPierre was paid $2.2 million by the NRA in 2018, the most recent year available, the nonprofit group’s public filings show. His total reported pay from 2014 to 2018 was $11.2 million.

In August, he was charged in a civil suit by New York Attorney General Letitia James with taking millions of dollars of allegedly undisclosed compensation from the NRA and its vendors, in the form of free yacht trips, private jet flights for his family, exotic safaris and other benefits.

Asked at a news conference announcing the lawsuit whether she believed Mr. LaPierre had evaded personal taxes, Ms. James declined to comment but said she was referring the matter to the IRS.

The AG lawsuit claimed the NRA’s failure to include certain personal benefits in Mr. LaPierre’s W-2 annual-compensation forms “permitted him to file false personal tax returns with the IRS.”