"I have today written to president Zuma to re-state that the Constitution requires proper and meaningful consultation before he decides on an appointment," she said in a statement.

"In the past, the president has 'consulted' at the very last moment, as a formality, when his mind was clearly already made up."

She said this prevented opposition parties from having a fair chance to engage with Zuma on his choice.

Zille suggested that the full candidate short-list be distributed to party leaders and that a "reasonable timeframe" be allowed for submissions on the candidates.

"The president should apply his mind to the points raised in the submissions, and be prepared to motivate for his preferred candidate," she said.

Zille said Zuma had never replied to written submission about judicial appointments.

"Judicial appointments are one of the most important functions of the president," she said.

"If he wants the appointments to have credibility, he must consult meaningfully and with an open mind, as we believe the spirit of the Constitution requires."

The Judicial Service Commission (JSC) said on June 12 that Zuma had been presented with a list of nominees for the vacant judge's position in the Constitutional Court.

Chief Justice Mogoeng Mogoeng presented the list of names to Zuma following interviews with four candidates.

Judges Lebotsang Bosielo, Mandisa Maya, Robert Nugent and Raymond Zondo were those listed for the vacancy.

In terms of the Constitution, Zuma must notify the JSC if he finds any of the nominees unacceptable and he must motivate his reasons.