The right-wing opposition party that controls Peru's Congress called for President Pedro Pablo Kuczynski to resign by the end of Thursday after Brazilian builder Odebrecht reported transferring $4.8 million to companies linked to him.
Kuczynski has denied any improper earnings and offered to answer questions before a congressional committee next week.
Daniel Salaverry, a congressman and spokesman for the Popular Force party that has an absolute majority in Congress, did not say what would happen if Kuczynski failed to heed the end-of-day "deadline" that he said several parties had agreed to give him.
However, a leftist party, Frente Amplio, said earlier on Thursday that it was preparing a motion to oust Kuczynski. Popular Force and Frente Amplio together have 82 seats in Congress.
Eighty-seven votes would be needed to oust Kuczynski, 79, a former Wall Street investor narrowly elected last year.
On Thursday, Odebrecht provided a report that Congress had requested that showed transfers of about $780,000 to a company Kuczynski controlled during and after he held senior government roles, and of $4 million to a company headed by a close associate of Kuczynski's in following years.
As late as last month, Kuczynski had strenuously denied ever taking any money from Odebrecht or having any professional links to the company.
Odebrecht is at the center of Latin America's biggest graft scandal and has admitted to paying about $30 million in bribes to officials in Peru over a decade, including during the 2001-06 term of ex-President Alejandro Toledo, when Kuczynski was finance minister and prime minister.
"It's clear his permanence in the nation's highest office is unsustainable due to proof of corrupt acts," Salaverry told a news conference.
Kuczynski's office has declined requests to comment on the report Odebrecht sent to Congress.
"There are a lot of rumors," Kuczynski said Thursday in a speech at a military ceremony without directly addressing the Odebrecht disclosure. "We need to unite together against real obstacles."
The escalating political instability has spooked markets in the world's second-biggest copper producer and one of the region's most stable economies. Peru's sol currency closed 0.31 percent weaker against the dollar amid the instability, and the Select stock index closed 3.5 percent lower on Thursday.
Popular Force spokesman Salaverry called for Kuczynski's first vice president, Martin Vizcarra, to replace him when he resigns.