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 South African rand dropped sharply on Wednesday as a fractious budget vote threw into doubt the solidity of the coalition government. At 1640 GMT, the rand traded at 18.7725 against the dollar, about 1.