Malawi's president, Peter Mutharika, on Tuesday refused to ratify bills to pave the way to new polls after his re-election last May was annulled over irregularities.
The Constitutional Court last month ordered officials to hold fresh presidential elections within 150 days, but the bills for doing so require Mutharika's assent.
Spokesman Mgeme Kalilani announced the president's decision at a press conference on Tuesday.
"It is the president's opinion that most of the provisions being proposed are in sharp contradiction with Malawi's constitutional order," Kalilani told AFP after the briefing.
"Any law or amendment to the law that is inconsistent with the constitution shall be invalid," he added.
The proposed amendments requested a more than 50 percent majority to secure a second term -- a major sticking point for Mutharika, who was declared winner with just 35.8 percent of the vote.
Without his approval, the draft laws will be returned to the National Assembly.
It is the first time a presidential election has been challenged on legal grounds in Malawi since independence from Britain in 1964.
Mutharika is attempting to quash the process.
He has filed an appeal against the court's annulment of the results and refused to fire members of Malawi's electoral commission, as recommended by parliament.
"(Their) report has failed to establish that members of the committee... lack competence and capacity," said Mutharika in a statement read out by his spokesman.
"I find this position specious and laughable."
Malawi's Supreme Court is expected to rule on Mutharika's appeal in April.