Zille said on Friday her office was seeking legal advice on whether she had been "unconstitutionally excluded" from the JSC committee that met on the Hlophe issue last week.

After that meeting, the JSC announced that it was dropping its probe into a misconduct complaint against Hlophe, who is Western Cape judge president.

Zille's announcement followed a piece published earlier in the day by constitutional law expert Pierre de Vos, on his blog Constitutionally Speaking.

In it, De Vos asked whether Zille should have been part of the committee when it made that decision.

"A clever and alert reader of this blog thinks so - and I agree," he said.

"This would mean the JSC was unlawfully constituted when it made its decision and on that ground alone the decision could be set aside by a court," he said.

He said section 178(k) of the Constitution laid down that when the JSC considered "matters relating to a specific high court," the premier of that province or her representative had to form part of the body.

Premiers already formed part of the JSC when it decided on appointments for the high court in their provinces, so the composition of the high court was deemed to be "a matter relating to a high court".

"It seems to me that it follows by necessary implication that if the premier is involved in the appointment of any judge, he or she must also be involved in the possible removal of any judge," De Vos said.

On Thursday a civil rights body, Freedom Under Law, which is headed by former Constitutional Court judge Johann Kriegler, said it intended challenging the JSC decision.

Kriegler told journalists proceedings would be launched soon to set aside the decision as "irrational and unreasonable".

The challenge by Freedom Under Law has the support of two of its panel members, Desmond Tutu and Mamphela Ramphele.

Sapa