BUENOS AIRES (Reuters) - Argentina's Supreme Courtdealt a blow to a controversial anti-monopoly broadcast reformlaw Tuesday, upholding an earlier ruling that said mediacompanies should not have to sell off certain operations withina year.

The government-backed law was passed last year, deepeningan acrimonious dispute between President Cristina Fernandez andleading media group Grupo Clarin, owner of Argentina's biggestnewspaper and most-watched cable news channel.

Grupo Clarin is seen as one of the media organizations thatstands to lose the most from the law, which center-leftFernandez says will break up monopolies and open the country'sairwaves to new voices.

The law had ordered media groups to sell off someoperations if there was judged to be a concentration ofownership in certain sectors, such as cable television.

Tuesday's Supreme Court decision, detailed in a statement,effectively upholds an earlier lower court ruling to suspend anarticle of the law that obligated the companies to sell someholdings within a year.

This suspension remains in effect while the lower courtdecides whether the law is constitutional.

The media law has faced a series of legal challenges sinceit was passed a year ago.

Fernandez's battle with Grupo Clarin has strained relationswith business leaders, who have been increasingly critical ofher government in recent months. (Reporting by Nicolas Misculin; Writing by Helen Popper;Editing by Bill Trott)