The logo of America Movil is pictured on the wall of a reception area in the company's corporate offices in Mexico City, Mexico, May 18, 2017. REUTERS/Edgard Garrido

MEXICO CITY (Reuters) - Mexico's Supreme Court ruled on Wednesday in a spat over interconnection rates paid between telecommunications firm America Movil AMXL.MX and rivals that touches on a bigger case related to an antitrust reform the company is fighting.

Long-dominant America Movil, controlled by billionaire Carlos Slim, is challenging several aspects of a 2013-14 telecommunications reform that opened the door to more competition in the industry.

On Wednesday, the court ruled partly in favor of a unit of America Movil against Pegaso PCS and Grupo de Telecomunicaciones Mexicanas, both of which are units of Telefonica TEF.MC, in a case involving rates charged to interconnect calls between their networks in 2015.

After the industry reform went into effect in late 2014, it was too late to resolve disagreements over an interconnection rate for the following year, so the rate from 2014 was adopted by regulators.

The Supreme Court said that was wrong. But it also said that under a newly negotiated rate for 2015, the amounts of money previously paid between companies would have to be adjusted to adhere to the newly determined rate.

The case was just one of several the Supreme Court is considering that relate to the telecom reform.