President Michel Temer of Brazil has denied a newspaper report that he approved payments to silence a possible witness in a corruption inquiry.
He was accused of authorising illicit payments to a jailed former speaker of the lower house of the Brazilian parliament, Eduardo Cunha.
Cunha was sentenced in March to 15 years in prison for corruption, money laundering and tax evasion.
The accusations against Mr Temer were made by O Globo newspaper.
A massive game-changer: analysis by Julia Carneiro, BBC News, Rio de Janeiro
The content of the alleged recordings is so grave that the shockwaves quickly rippled across the country.
There was turmoil in Congress, with opposition members calling for snap elections and filing at least two official impeachment requests against President Temer, within hours.
Protesters took to the streets in Sao Paulo and Brasilia, calling for the president to resign.
There was also loud pot-banging from windows in cities like Rio de Janeiro, Salvador and Recife.
On social media, the question of what will happen now is being asked, while on Brazil's main news channel political, commentators have referred to this as a "point of no return". President Temer denied the allegations and called for them to be thoroughly investigated.
Whatever the outcome, this is a massive game-changer - the first time Mr Temer has been directly implicated in the massive corruption inquiry known as Car Wash. The effect will be even more damming should the audio of the recording be made public.
Mr Temer, a former law professor, played a key role in the impeachment proceedings against his predecessor, President Dilma Rousseff, last year.
As vice-president, he replaced her after she was impeached and removed from office.
'Nothing compromising'
O Globo says it has obtained recordings of a discussion between Mr Temer and an official from the giant meat-packing company JBS.
The newspaper says the tapes were presented in plea bargain negotiations between prosecutors and two JBS executives.
Mr Temer's office says the allegations are false and is calling for them to be thoroughly investigated.
"President Michel Temer has never requested payments to obtain the silence of former MP Eduardo Cunha," it said.
"He did not participate in, nor did he authorise, any movement with an aim to avoid that the former congressman make a plea bargain deal or co-operate with justice."
It confirmed that a meeting with a JBS executive had taken place in March but said "there was nothing in the dialogue that would compromise the President's conduct".