Congressional investigators are questioning a half-dozen lawmakers for possibly misspending government funds meant to pay for overseas travel, according to people familiar with the matter.

The investigation follows a Wall Street Journal article in March that said lawmakers had used daily cash stipends, meant to cover certain costs of official government travel overseas, to cover expenses that appeared to be unauthorized by House rules. An independent ethics board has referred the matter to the House ethics committee.

Congressional rules say the daily travel funds, called a per diem, must be spent on meals, cabs and other travel expenses. But when lawmakers travel, many of their meals and expenses are picked up by other people, such as foreign governmentofficials or U.S. ambassadors.

That can leave lawmakers with leftover money. Lawmakers routinely keep the extra funds or spend it on gifts, shopping or to cover their spouses' travel expenses, according to dozens of current and former lawmakers.

The cash payments vary according to the cost of living and range from about $25 a day in Kabul to more than $250 a day in one part of Japan. Lawmakers also usually request and receive an additional $50 a day. Leftover funds can add up to more than $1,000 a trip for longer visits to expensive regions.