The Democratic Alliance has given President Jacob Zuma 72 hours to answer questions on his new home or face legal action.
"We asked them for details on how much was spent, on what, by whom, and under what provision of law," the party said in a statement on Sunday.
"If there is no substantive response by close of business on November 7, we will instruct our lawyers to make preparations to take him and the government to court."
The DA said it had not yet received a response, only a receipt of the letters.
A large group of ANC supporters sang as they waited for DA leader Helen Zille to leave the Nkandla police station on Sunday.
She laid a charge under the Gatherings Act against the ANC for blocking a public road during her failed attempt to visit President Jacob Zuma's KwaZulu-Natal homestead.
When the convoy transporting the Democratic Alliance and a media contingent left the satellite police station, ANC shouted "hamba" (leave).
An ANC supporter was arrested for drunk and disorderly outside the police station.
Police spokesperson Colonel Jay Naicker said another man was arrested earlier, during a demonstration by ANC supporters, for having an unlicensed firearm. "The man was in possession of a rifle. He will be charged for discharging a firearm in public and possession of a firearm."
'Lost the right'
Zille said Zuma had lost the right to call his home a private residence. "Nkandla belongs to each and every South African who has to sacrifice the basic services they need, so that the president could turn his home into a five-star fortressed palace.
"One day we will look at it as a monument to the fight against corruption."
She questioned how the government could spend R248-million on Zuma's home, when it would not pay to transport the relatives of the victims of the Marikana shooting to the Farlam commission of inquiry.
Earlier police stopped her and her entourage from approaching Zuma's homestead, in the village of KwaNxamalala, saying they wanted to prevent violence. Zille was told she could not pass the police roadblock as there were ANC supporters on the road to Zuma's home.
She said the party had permission to gather on a public road outside a school opposite Zuma's home. Several cars carrying ANC supporters passed the police roadblock on a side road. They carried sticks and sang Dubhula ibhunu (Shoot the Boer).
Buses full of ANC supporters were allowed to pass on the main road. When Zille asked officers why they were allowed to pass, she was told they would open a case against the organisers of the ANC march. "We never intended to go inside Zuma's home, we only wanted to gather opposite his compound on a public road," Zille said.
About 700m from where the Democratic Alliance was stopped, police in riot gear prevented ANC supporters from advancing. Officers formed a human chain across the road. Police had several armoured Nyala personnel carriers, two trucks with water cannons, and a helicopter in the area.
The DA had wanted to visit Zuma's private residence, where an upgrade, reportedly costing over R200 million, and funded with taxpayers' money, was in progress.
– Sapa, M&G Reporter