Mexico’s antitrust regulator has blocked an alliance formed by three supermarket retailers to compete against retail giant Wal-Mart de Mexico (Walmex).

Mexican retailers Gigante, Soriana and Comerci formed a joint purchasing venture called Sinergia last year which aimed to obtain better prices from suppliers so that the retailers could better compete with Walmex,

“The creation of Sinergia was rejected,” a high-ranking official in the government’s Federal Competition Commission, or CFC, was quoted by Reuters as saying.

Walmex is majority owned by US retail titan Wal-Mart.