PHILADELPHIA — A Pennsylvania man is suing health insurer Aetna, saying his sister learned he was taking HIV medication after the company mailed him an envelope with a large, clear window that showed information on where to purchase the drugs.

The lawsuit filed Monday in U.S. District Court in Philadelphia is seeking class-action status.

It says the 52-year-old man from suburban Philadelphia doesn’t have the virus that causes AIDS but was taking the medication preventatively.

The lawsuit claims the mailing violated the law by revealing HIV information of about 12,000 customers in at least 23 states.

A spokesman for the Hartford, Connecticut-based company declined to comment on the suit.

Last week, the company said it was reviewing processes to ensure such a mistake never happens again.