BENTONVILLE, Ark. (AP) — Wal-Mart Stores Inc. is alerting its global suppliers that it will immediately drop them if they subcontract their work to factories that haven't been authorized by the discounter.

In a letter sent Tuesday to suppliers of its Wal-Mart stores as well as Sam's Clubs in the U.S., Canada and the United Kingdom, the company says it will adopt a "zero tolerance" policy on subcontracting without the company's knowledge, effective March. 1.

Previously, suppliers had three chances to rectify their mistakes.

Wal-Mart's stricter measure, along with other changes to its policy, comes amid increasing calls for better safety oversight after a deadly fire at a Bangladesh factory that supplied its clothes. Wal-Mart has said that the factory should not have been making its clothes.