The public protector will look into the distribution of food parcels in Tlkowe by Social Development Minister Bathabile Dlamini, her office said on Monday.
The matter would be investigated under the Executive Members' Ethics Act, spokesperson Oupa Segalwe said.
"Under this law, the public protector does not have the discretion on whether or not to investigate," he said.
Democratic Alliance (DA) MP Mike Waters sent protector Thuli Madonsela a letter on September 13, asking her to investigate Dlamini.
The DA accused Dlamini of trying to buy votes ahead of municipal by-election in Tlokwe, North West, by dishing out food parcels.
Dlamini's visit came a few days before a by-election in Tlokwe's Ward Nine.
At the time, Dlamini denied that this was the reason for the relief efforts, and said there were more than 17 000 child-headed households in Tlokwe (Potchefstroom).
The ANC recently won two of three municipal by-elections in Tlokwe, according to results released by the Independent Electoral Commission.
The party's candidate Oupa Mogoshane lost Ward 26 to former ANC councillor Batiki "Stone" Mahlabe, who stood as an independent candidate.