Argentina's government told the country's largest media conglomerate on Monday that it has begun to assert control over the company and auction off its media licences.
Grupo Clarin is one of the government's leading critics and has battled with President Cristina Fernández for years. Fernández argues that it is a corporate monopoly and has funded a booming network of pro-government newspapers and stations to challenge Clarin's dominance.
Martin Sabbatella, the head of the government media regulation body, said on Monday that the government would make the conglomerate and other companies comply with the law, which bars any company from owning too many different media properties.
It comes after a court ruled Friday that a three-year-old law against media monopolies is constitutional.
"We notified them of the start of the transfer of licences because the law is constitutional," Sabbatella said at an impromptu press conference outside Grupo Clarin's headquarters in Buenos Aires.
Grupo Clarin said in an emailed statement that the government's action was illegal and trampled on past rulings that favoured the media group.