The ANC's national executive committee agreed that people join the party voluntarily and are bound by its policies, secretary-general Gwede Mantashe said on Monday.
He was referring to the two African National Congress MPs who did not vote for the Protection of State Information Bill in Parliament last week.
"The conduct of members acting as free agents is a non-option. Equally public representatives of the ANC are holding public offices at the instance of the ANC," Mantashe told reporters in Johannesburg.
"They are therefore bound by policy directives of the ANC and not their whims and thoughts."
Mantashe said he did not know what action would be taken against the two MPs.