The PAP news agency said KNF chief Marek Chrzanowski denied the newspaper reports and quoted him as saying that he was resigning out of "a sense of responsibility for the functioning of regulatory supervision over the financial sector".
Chrzanowski did not immediately reply to requests for comment from Reuters.
Prime Minister Mateusz Morawiecki earlier demanded an investigation of reports that Chrzanowski asked Getin Noble Bank to hire a specific lawyer and pay him a salary equal to one percent of the bank's capitalisation, around $10.5 million.
In return the mid-tier lender would receive "support" from the regulator, the Polish daily Gazeta Wyborcza and the Financial Times reported, citing a deposition to Polish prosecutors from Getin Noble Bank's owner, Leszek Czarnecki.
Reuters has seen a copy of the deposition.
The prosecutor's office confirmed that a representative of Czarnecki had notified it that he suspected a crime had been committed related to corruption.
Getin Noble Bank declined to comment.
KNF denied any wrongdoing and said information regarding an offer by its chairman to favour Getin Noble Bank in exchange for a payment of around 40 million zloty ($10.5 mln) was not true.
"Such a proposal was not offered during any meeting with Mr Czarnecki," a KNF spokesman said in a statement.
The lawyer named in the deposition, Grzegorz Kowalczyk, said the first he had heard about the allegations was in the media.
"I have never consented to anyone seeking a job for me at Getin. I have never talked to Leszek Czarnecki. I know Marek Chrzanowski privately," he told Reuters.
Chrzanowski, a former central banker, was nominated to his post in 2016 by the ruling Law and Justice (PiS) party, which has said one of the pillars of its fiscal policy is fighting corruption in value-added tax collection.
Before his reported resignation, the prime minister summoned Chrzanowski to a meeting on Wednesday with the minister responsible for Poland's secret services, the head of the prime minister's office, Michal Dworczyk, said on Twitter.
"The prime minister has asked the services and the prosecutor's office to take quick and decisive action in order to check and clarify information concerning the KNF chairman", government spokeswoman Joanna Kopcinska said.
Shares in Getin Noble Bank, which is Poland's no. 9 lender by assets, have fallen 66 percent this year, and were down by more than 5 percent by 1545 GMT.
The bank has a credit portfolio with a significant number of bad loans, some of them foreign-currency denominated. Czarnecki had promised to pump one billion zlotys into the bank this year and next.
($1 = 3.8174 zlotys) (Additional reporting by Anna Wlodarczak-Semczuk; editing by Nick Tattersall and Jon Boyle)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)