Mexican immigrant groups in the United States threatened Tuesday to boycott telephone companies owned by Mexican mogul Carlos Slim to protest what they say are abusive charges. "Carlos Slim's monopolistic practices have imposed significant costs to the Mexican economy and burdened the people of Mexico and Latin America," said Juan Jose Gutierrez, of the nonprofit organization VAMOS Unidos USA. Gutierrez, speaking at a news conference at the National Press Club in Washington, said there was a protest campaign under way across the country aimed at Slim's tight grip on Mexican telecommunications. The groups have forged a coalition called "Two Countries One Voice" and have demanded that George Washington University (GWU) sever its ties to Slim, who received the school's President's Medal in 2009 for his philanthropic work. Slim is due to receive an honorary degree from the Washington-based university on May 20 in a graduation ceremony on the National Mall. In a letter to Steven Knapp, the president of the university, the coalition said: "George Washington University should not continue to honor a man that has amassed his fortune on the backs of the people of Mexico and Latin America." "We're giving them 48 hours. We're going to keep our options open if they don't respond to us," said Andres Ramirez, an activist from Nevada. A GWU spokesperson, in an email to AFP, said that "the university is looking forward to Mr. Slim's participation in commencement." Considered the world's richest man, Slim heads Mexico's two main telecoms, Telmex and Telcel. Mexican antitrust authorities recently suspended a fine of 11.9 billion pesos (about $920 million) imposed on Telcel a year ago, in exchange for pledges to lower its connection rates to other operators. The top US trade envoy also signaled concerns about Telcel fees in an annual report last year. Mexico is the principal destination of international calls originating in the United States.