"Treatment Action Campaign (TAC) will pursue litigation for a national treatment and prevention programme," TAC spokeswoman Siphokazi Mthathi told Agence France Presse.
The announcement came ahead of the four-day South African AIDS Conference 2003 opening in the eastern coastal city of Durban Sunday evening.
TAC has for months been urging the government to announce the start of a national treatment plan to help those infected with HIV/AIDS. The group argues that the expense of anti-AIDS drugs would be less than the long-term costs of dealing with the effects of the disease.
Almost 1,000 deaths per day
South Africa has one of the highest AIDS rates in the world with 360,000 deaths in 2001, an average of 986 per day, according to UN agencies.
"TAC has decided to go back to a civil disobedience campaign as a strategy to insist on treatment," Mthathi said while attending a weekend TAC congress in Durban.
South Africa has an estimated 4.7 million people infected with HIV/AIDS out of a total population of around 44 million.
HIV/AIDS is expected to cut South African life expectancy from an estimated 59.9 years in 1990 to 45.2 years in 2005.
13 percent of South African children were estimated to be orphans in 2002, many of them because of HIV/AIDS.
An estimated three percent of South African households are currently headed by children.
The group had suspended a similar earlier campaign after the government promised to look into its demands for a national treatment plan.
Critics say South Africa's government has moved far too slowly on AIDS/HIV. The government's refusal to permit public sector hospitals to use anti-retroviral drugs, the only medicines proven effective against AIDS, has stoked anger.
Government officials led by Health Minister Manto Tshabalala-Msimang have questioned the drugs as unproven and potentially toxic, a position widely challenged by scientists and AIDS activists.
Tepid government response
"We want to believe the government is committed and has the best interest of our people at heart, but we are not seeing that, we are not getting it, so we are preparing to make sure we get that kind of leadership," said Mthathi.
If the legal action goes ahead, it would be the second time TAC has challenged government AIDS policies in court. The lobby group won a high court order 16 months ago, forcing the state to provide antiretroviral drugs to pregnant women.
"We want to believe the government is committed and has the best interest of our people at heart, but we are not seeing that."
-TAC spokeswoman Siphokazi Mthathi
That order is the subject of controversy at the moment, since South Africa's Medicines Control Council (MCC) is threatening to ban the antiretroviral drug nevirapine, used in mother-to-child transmission prevention.
Mthathi said a global petition, launched by the Washington-based Elizabeth Glaser Paediatric Aids Foundation, would be presented at the AIDS conference to protest the threat to ban the drug.
The MCC has said it may ban nevirapine because it believed the paperwork in a key Ugandan study to be defective - despite the drug being endorsed by the World Health Organisation and UNAIDS.
TAC chairman Zackie Achmat is currently refusing to take medication in protest of the government's lack of action - despite reports that his HIV-positive condition is nearing full-blown AIDS.
Mthathi said TAC members attending the organisation's weekend congress had urged Achmat to reconsider his protest action.
"We need to keep our leaders alive. They are the people who are working to ensure that the rights of other HIV-positive people. It doesn't help us if our leaders die.
"Zackie is trying to keep it together but he needs treatment. He's walking and he's alive but he won't be strong for a long time," Mthathi said.