The case is being prepared by a group of lawyers for the country's opposition coalition, said Gerardo Blyde, a lawyer and opposition politician. He told reporters on Saturday that it's not yet clear when the case will be brought before the Costa Rica-based Inter-American Court of Human Rights.
The opposition's announcement came three days after the Supreme Court's decision. Despite opposition claims that the constitution requires the inauguration to be held on Jan. 10, the pro-Chavez congress approved delaying the swearing-in and the Supreme Court endorsed the postponement, saying the president could take the oath of office before the court at a later date.
The government says the 58-year-old president, who is starting a new term after being re-elected in October, is fighting a severe respiratory infection in a Cuban hospital. Chavez underwent his fourth cancer-related surgery on Dec. 11, and he hasn't spoken publicly or been seen since.
The opposition has demanded more information about Chavez's condition, and some have called for a medical team to be formed to determine whether he is fit to remain in office.
Chavez's elder brother, Adan, the governor of their home state of Barinas, returned to Venezuela on Friday after a visit to Havana and his office's website posted a statement saying the president "continues assimilating his treatment in a good way and every day he advances with his recovery." Adan Chavez declined to give details, saying the vice president is in charge of providing updates on the president's condition.
Blyde, a district mayor, spoke to reporters at an outdoor gathering in a city plaza where leading Chavez opponents denounced the Supreme Court's decision before a small crowd. One woman held a sign demanding of the government: "Tell the truth."
The court's ruling made impossible any appeal within Venezuela, so the opposition decided to seek relief from the regional tribunal. Blyde said the Supreme Court ruling violated democratic rules laid out in the 2001 Inter-American Democratic Charter.
Chavez's government has repeatedly clashed with two regional human rights bodies. It began a process of pulling out of the human rights court in September when it notified the Organization of American States that it was renouncing a regional convention on human rights.
But Blyde noted that the Venezuelan government will continue to be a party to the human rights court for a yearlong period that will end this September.
There was no immediate response from the government about the planned challenge before the regional court. Vice President Nicolas Maduro was visiting Cuba on Saturday, and had said he would be meeting with Chavez's family and medical team.