Mexico's Federal Competition Commission issued a warning to two of its biggest brewers to open up the market to other competitors or face heavy penalties.

According to the initial report, the penalty could reach as much as eight percent of the total revenues of the companies each year.

The warning was prompted by the complaint of SABMiller--which carries Miller, Peroni and Grolsch brands-to enter the market because of the exclusivity deals of both Grupo Modelo and Cuauhtemoc Moctezuma with local stores and restaurants.

Cuauhtemoc is owned by Heineken Holding NV, maker of the popular Heineken beer, while Modelo is a unit of the Belgian-Brazilian firm, Anheuser-Busch InBev, maker of Budweiser and Corona beers.

In answer to the commission's warning, the two companies agreed to scale down the exclusivity deal to a quarter percent in points of sale and cutting it further to 20% over the next five years.