South African opposition party the Economic Freedom Fighters (EFF) has written to the speaker of parliament seeking to block lawmakers from meeting on Wednesday to vote on the next stage of the budget process.

The EFF said in a letter to National Assembly Speaker Thoko Didiza that Tuesday's proceedings at a key parliamentary committee, which supported the fiscal framework despite reservations about some budget revenue-generating measures, were "procedurally defective and vulnerable to legal challenge".

It asked for the committee's report supporting the fiscal framework to be withdrawn and for a Wednesday afternoon sitting of parliament to consider and vote on the report to be rescheduled.

"Should this not occur, the EFF ... will consider urgent legal steps, including the possibility of an interdict, to prevent the tabling and processing of a report adopted in violation of the law," the letter said.

The biggest political party in the ruling coalition, the African National Congress (ANC), relied on the small party outside the coalition, ActionSA, to get the support it needed on Tuesday in parliament's Standing Committee on Finance.

The ANC's main coalition partner, the Democratic Alliance has accused it of crossing a "line in the sand" by using a party outside the coalition to get the fiscal framework approved.

The country's biggest trade union group Cosatu, a longstanding ANC ally, said it would be a "travesty" if parliament's reservations about raising value-added tax and not adjusting personal income tax brackets for inflation were ignored.

It said in a statement: "That will be a calamity and breach of trust that politicians heading into the 2026 local elections dare not play with."