Mexico's Federal Competition Commission, or CFC, said it imposed a fine of 653.2 million pesos (about $50 million) on state-owned oil giant Petroleos Mexicanos, or Pemex, for forcing service stations to hire the oil monopoly's trucks to handle deliveries of gasoline and diesel.

The practice forced service stations to "pay a surcharge amounting to 1 billion pesos (about $77 million)," the CFC said in a statement.

The fine was approved on a vote of 3-2 by the CFC's commissioners and the agency ordered Pemex to "cease this practice within 30 working days."

Pemex Refinacion is responsible for 651.6 million pesos of the total fine for engaging in monopolistic practices in the market for the transportation of gasoline and diesel, the CFC said.

Pemex will have to pay the remaining 1.6 million pesos "for assisting in said practices," the CFC said.

Under Article 27 of the Mexican Constitution and implementing legislation, Pemex Refinacion is the country's only authorized wholesaler of gasoline and diesel.

The company, however, "abused the market power that this legal exclusivity grants it by forcing service stations to acquire" gasoline and diesel from the company itself once the fuel was no longer under its ownership, the CFC said.

Pemex has a monopoly on the production of oil and gas, as well as over the production of petroleum derivatives and the distribution of gasoline, in Mexico.

The state-owned oil giant, which posted total revenues of $131.75 billion and had assets of $161.8 billion in 2012, is the world's No. 5 oil producer and accounts for about 40 percent of the Treasury's revenues. EFE