South Africa’s fragile unity government has been shaken again. The country’s second-largest political party broke with partners Wednesday and voted against a national budget.

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 rand is under pressure as markets sit on edge, waiting to see what happens with the crucial budget vote on Wednesday—and what it means for the future of the GNU.