South African opposition party the Economic Freedom Fighters 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 Democratic Alliance, which joined the government after the long-ruling African National Congress lost its parliamentary majority last year, said it could not support a tax increase that would further burden the poor majority of the country’s population.

South Africa’s coalition government is on the brink of collapse after a leading party broke ranks and voted against the Finance Minister’s budget, forcing the long-ruling African National Congress to rely on smaller parties for support.