"We shall spare no effort in seeking to determine the motive behind this unacceptable and inexcusable conduct … " ANC spokesperson Jakson Mthembu said in a statement on Tuesday.
The move was "clearly designed" to hand over the municipality to the opposition "at all cost", he said, after the mayor was unseated for a second time on Tuesday.
It included undermining democratic process and disregarding the wishes of the people.
"The ANC is deeply angered by its councillors involved in this matter for their appalling and unacceptable behaviour, which is clearly an act of defiance and a calculated effort to bring shame and embarrassment to the organisation," said Mthembu.
Democratic Alliance (DA) councillor Annette Combrink was voted in as the new mayor – also for a second time – on Tuesday.
DA North West leader Chris Hattingh said 29 councillors from all parties, including the ANC, had unanimously voted to return Combrink to the position of mayor.
"This [was] after the failure of former mayor Maphetle Maphetle to deal with damning forensic audit findings of corruption," he said.
Motion of no confidence
Mthembu said the ANC would invoke its "disciplinary tools" against its councillors.
"This desperate and atrocious behaviour occurs at a time when the councillors involved are currently undergoing internal disciplinary processes of the ANC for the first time they committed the same offence," he said.
In November, ANC factions in the municipality passed a motion of no confidence in Maphetle.
He was replaced by Combrink – the first DA mayor in the province – when she defeated ANC candidate Lucky Tsagae by 20 votes to 19.
However, Maphetle was returned as mayor in February when he won by 31 votes to Combrink's 21 votes.
While the DA was in charge, it requested a forensic investigation into irregularities at the municipality.
The probe found that the council irregularly bought Maphetle a R736 000 customised Mercedes-Benz. Maphetle allegedly abused the Disaster Management Fund and Poverty Relief Fund.
The report recommended that formal disciplinary action be taken against him and other officials.
In May, the DA laid criminal charges against Maphetle, and in June, Public Protector Thuli Madonsela said she would investigate the claims of corruption involving Maphetle.
The ANC in North West said it was regrettable that some its caucus members in Tlokwe had "conspired with the opposition in the irregular removal" of Maphetle.
"Our view is that the ANC councillors in Tlokwe behaved in a manner that is against the ANC principles and constitution," the party said.
"The ANC will meet with its legal representative to seek recourse on the matter, as we are of the firm view that the removal of the mayor is irregular."
Hattingh said the DA welcomed the "united front" against corruption shown by the municipality.
"The DA is the only political force that can bring stability to the municipality, given the severe divisions within the ANC.
"We will now act immediately to deal with key delivery issues, such as housing, which is being affected by unsafe dolomite rocks beneath the surface threatening to collapse and endanger residents," he said.
Hattingh said Combrink appointed a mayoral committee within minutes of being elected – something the DA claimed the ANC had failed to do in three months of office. – Sapa