The African National Congress (ANC) is trying to turn the Judicial Service Commission (JSC) into a "thinly disguised party instrument", Democratic Alliance (DA) leader Helen Zille said on Friday.

"Last month, the Minister of Justice, Jeff Radebe, took the unprecedented step of bullying the JSC into postponing interviews for judicial appointments," Zille wrote in her weekly newsletter.

There could be little doubt the ANC demanded the postponement in order to win time to change the composition of the JSC to secure a majority of ANC appointees.

"The ANC is attempting to subvert the JSC by turning it into a thinly disguised party instrument," she said.

The newly constituted JSC - which nominates and recommends candidates for judicial appointments - would face its first major test in selecting replacements for four retiring Constitutional Court judges.

The ANC's "carefully crafted majority" on the JSC meant the party would be able to choose the new judges.

She said the ANC was also trying to take control of the judiciary through the proposed Superior Courts Bill.

The Bill could resurrect the government's attempts to bring the administration of the courts under the Minister of Justice, who is an ANC politician, Zille said.

"If the still-to-be-tabled legislation re-introduces the ANC's plan, which was withdrawn after a public outcry last year, it could result in the executive determining which judge should hear a particular case.

"This would completely undermine the independence of the judiciary," she said.