The two biggest warehouse retail chains, Sam’s Club and Costco Wholesale, are limiting how much rice customers can buy.Sam’s Club is a division of Wal-Mart Stores, but the broader chain has no plans to limit food purchases.

American rice futures are hitting record highs amid global food inflation, although one rice expert said the warehouse chains might be reacting less to any shortages than to stockpiling by restaurants and small stores.

Sam’s Club declined to say if this was first time it had restricted sales of bulk foods. The limits affect 20-pound bags, not retail-size portions. Costco could not immediately be reached for comment on its limits, which affect bulk purchases in some stores.

Sam’s Club said it would limit customers to four bags at a time of imported jasmine, basmati and long-grain white rice.

A Sam’s Club spokeswoman, Kristy Reed, said she could not comment on whether the problem had been caused by short supplies or by customers stocking up in anticipation of higher prices.

A USA Rice Federation spokesman, David Coia, said there was no rice shortage in the United States. A smaller chain, BJ’s Wholesale Club, said it was not imposing limits for now.