Payday loans company Wonga is investigating claims one of its employees called Labour MP Stella Creasy a "self-serving egomaniac" on Twitter.
According to an investigation by The Guardian Creasy, who has campaigned against payday lenders was criticised on Twitter as "mental", and "nuts" and a "self-publicist", by a now-closed Twitter account apparently traced back to Wonga.
Wonga said it was looking into the paper's claims, with a spokesperson telling The Huffington Post UK: "I can confirm that a direct apology has been sent to Stella Creasy. We are still conducting an investigation and we will take proper action."
The account, operating as @DanielSargant1, has since been deleted.
Reacting to the news, Creasy tweeted: "In this job, sometimes when people are out to get you, they really are out to get you. Wonga admits trolling me."
On Tuesday the Office of Fair Trading announced several payday lenders are facing formal investigations over the use of "aggressive debt collection" methods.
The OFT said that in several cases it had uncovered evidence that calls into question the continuing fitness of lenders to hold a consumer credit licence, which they need to trade.
David Fisher, OFT director of consumer credit, said: "We have uncovered evidence that some payday lenders are acting in ways that are so serious that we have already opened formal investigations against them.
"It is also clear that, across the sector, lenders need to improve their business practices or risk enforcement action."