The Economic Freedom Fighters said none of its more than 40 lawmakers will attend Thursday's speech after leader Julius Malema, deputy leader Floyd Shivambu and four other senior officials were barred from the legislature until the end of the month.
The announcement raises the stakes ahead of national elections later this year, when Ramaphosa's ruling African National Congress is facing the possibility of losing its parliamentary majority for the first time since coming to power at the end of the apartheid system of racial segregation in 1994.
Several polls have predicted the ANC, the party once led by Nelson Mandela, would get less than 50% of the vote. If those predictions materialize, it would be a major change for Africa's most developed economy.
The leftist EFF party was formed in 2013 and won just over 10% of the national vote in the last general election in 2019, but it was the only one of the three largest parties to increase its share of the vote.
The EFF says it represents poor Black South Africans who have been let down by 30 years of ANC rule.
The party and Malema have often courted controversy with their politics, which include proposed policies that underused land be taken away from some white people without compensation and redistributed to poor Black South Africans in an effort to right some of the wrongs of apartheid. The party has also called for the nationalization of South Africa's mines and banks.
Malema, Shivambu and the others who were suspended were part of a group of lawmakers who interrupted Ramaphosa's 2023 speech. When they were asked to leave, they instead rushed onto the stage holding signs saying Ramaphosa should step down. They were quickly bundled out of the room by security officials and police.
It was not the first time the party has turned rowdy, disrupting proceedings in Parliament and tussling with security officers.
Ramaphosa is expected to use his State of the Nation address to defend the ANC and his first term in office.
But South Africa has deep problems, including a shockingly high unemployment rate of more than 30%, a struggling economy, and an electricity supply crisis that has led to rolling power blackouts across the country of 62 million people, with disastrous effects on businesses.
The date for the elections hasn't been announced but it must be held between May and August.
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