Mexican Finance Minister Luis Videgaray has gone on national TV and radio to defend how he bought his luxury home.
His appearance follows Wall Street Journal reports that he bought the home from a construction firm whose parent company had won large public contracts.
Mr Videgaray is not accused of anything illegal and he says he will neither sell his home nor step down.
The affair comes in the wake of a similar case involving President Enrique Pena Nieto.
Last month, Mr Pena Nieto's wife was forced to sell a $7m (£4.4m) house she had bought from the same company and also made a televised address explaining the source of her income.
The Wall Street Journal says it has seen property records that show Mr Videgaray bought a luxurious home in Malinalco in the central State of Mexico from Bienes Raices H&G.
The firm's owner, Juan Armando Hinojosa, has other companies which have won public works projects worth hundreds of millions of dollars during President Pena Nieto's time in office, the newspaper says.
In a radio interview, Mr Videgaray said the home purchase was carried out with "honesty and legality".
The transaction took place before Mr Videgaray was finance minister.
"There was no conflict of interest," he said in a written response to the Journal.
"I did the deal when I was not holding public office and the deal was within market parameters."
However, BBC Mexico correspondent Will Grant says there are uncomfortable questions for the government and Mr Videgaray personally.
Among them are why he chose to finance the property through a minor mortgage lender belonging to Juan Armando Hinojosa, rather than a major Mexican financial institution.
Mr Videgaray has suggested that the government's reform agenda has disturbed vested interests in Mexico and that is why details of his personal finances are coming to light.
Mr Pena Nieto is facing the lowest popularity ratings of any president for many years, recent polls show.
He has faced severe criticism over his handling of the disappearance of 43 students in Iguala who were allegedly abducted by local police and handed over to a gang who murdered them.