Civil action groups called for Mutharika to resign over claims that he and the ruling Democratic Progressive Party (DPP) received about $195,000 (167,000 euros) from a contractor supplying food rations to Malawi police.
“The information we have been getting is very clear that the president benefitted from that transaction,” Gift Trapence of the Civil Service Organisations action group told AFP.
“If he does not resign after 14 days, we will take to the streets.”
Mutharika’s spokesman told local media that the president had done nothing wrong after the leaked Anti-Corruption Bureau (ACB) report was published in newspapers at the weekend.
ACB director Reyneck Matemba confirmed it was probing the contract over police food but declined to give further details.
“We are about to conclude our investigations,” he told AFP.
Malawi, one of the world’s poorest and aid-dependent countries, will hold presidential and parliamentary elections in May 2019.
Graft cases have recently rocked Malawian politics.
Mutharika was elected in 2014 after his predecessor Joyce Banda was embroiled in the “Cashgate” scandal when government officials siphoned off millions of dollars of public money.
Banda returned to Malawi in April after four years of self-imposed exile and said she was ready to run in the elections against Mutharika.
In April, thousands of Malawians took part in the country’s first nationwide anti-government demonstrations since 2011.
The marches, organised by civil action groups, were against alleged corruption and poor governance under Mutharika.