Holomisa's loyalty was to the ANC was suspect, and actions like his would increasingly undermine the authority of the party, NP spokesman Dr Johan Steenkamp said in a statement.
He was reacting to a statement by the Deputy Minister which the NP said was an explicit challenge to the wisdom of Mbeki wanting to regard a R50,000 cut to Sigcau from a R2 million bribe to her predecessor Transkei Prime Minister George Matanzima as "water under the bridge".
"He (Holomisa) brutally states that nothing has happened to change his view on this matter - not even Mr Mbeki's elaborate explanations.
"Nor does Mr Holomisa accept that `there was no further need for additional investigation concerning Minister Stella Sigcau' as concluded by Mr Mbeki," Steenkamp said.
It was clear that Holomisa was explicitly of the opinion that Mbeki was wrong and Sigcau corrupt.
"If this view resulted in him being sacked. `Let it be so!'. He has thrown down the gauntlet."
Steenkamp was referring to Holomisa's message to DP MP Douglas Gibson who called for his sacking in which the deputy minister said:
"If what I have said in the TRC (Truth and Reconciliation Commission) in Port Elizabeth on May 22 1996 regarding Minister Stella Sigcau's R50,000 from the R2m bribe by (Sol) Kerzner, is being constructed by Mr Douglas Gibson and others as ill-informed or malicious on my part, questions my sincerity and integrity and that such a behaviour warrants my sacking from the government: Let it be so! Who cares. Surely that would not be the end of the road for Holomisa."
It was clear that President Mandela's government faced its biggest palace revolution yet, Steenkamp said.
"In order to restore what remains of its credibility and international standing either Holomisa or Sigcau has to go - if not both.
"The truth must now be established expeditiously and the culprit must leave, Mr Mbeki cannot afford more bungling."