Conservative Party chairman Grant Shapps has denied claims he repeatedly edited entries about himself and other MPs on Wikipedia.
Mr Shapps told the BBC the allegations - reported by the Guardian - were "categorically false and defamatory".
"It is the most bonkers story I've seen in this election campaign so far," he said.
The Guardian claims Wikipedia has blocked an account it suspects is being used by Mr Shapps.
Entries in the online encyclopaedia are written and edited by its own readers. Creating a fake online identity to mislead other people - known as "sock-puppetry" - is banned.
The Guardian reports that Wikipedia barred a user called Contribsx from making further changes after its volunteer "administrators" found the account had systematically removed references to Mr Shapps' past business activities.
The administrator reportedly told the paper they believed the account was "either run by Shapps directly" or by someone else "but under his clear direction".
According to the Guardian, a third of the contributions were made to Mr Shapps' own Wikipedia entry and the rest were "largely unflattering changes" to the pages of other political figures.
Speaking to the BBC News Channel, Mr Shapps strongly rejected the allegations and said "nobody has ever been authorised to make such changes".
He said: "One editor, who for all we know is part of a Labour/Guardian smear campaign, has given a statement to the Guardian from which they seem to have based an entire story."
He added it was "pretty despicable" 15 days before the election and that he would write to Wikipedia's HQ in California to complain.
A source close to the politician told the BBC's Newsnight they could prove that on four occasions he could not have made the changes in question, providing details of Mr Shapps' whereabouts.
"A simple look in my diary shows I was elsewhere," Mr Shapps told the BBC.
Mr Shapps has faced media scrutiny of his business interests before he became an MP in 2005, including a series of self-help business guides he published on the internet under the pseudonym Michael Green.
Conservative colleagues have rallied behind Mr Shapps. Mayor of London Boris Johnson said the claims were a "load of nonsense" while Education Secretary Nicky Morgan said it was "completely unbelievable" he would do anything of the sort.
Speaking on Wednesday at an election event in Bedford, Prime Minister David Cameron was asked if he had confidence in Mr Shapps.
"Grant does a great job, he's made a very clear statement about this, and I have nothing to add," Mr Cameron said.
Asked about the claims, Lib Dem leader Nick Clegg said he was "prepared to believe" that Mr Shapps had not altered his Wikipedia entry but joked: "It just could have been someone else - Michael Green, for instance."
Newsnight reported that Mr Shapps is considering a complaint against the Guardian and consulting on whether the paper had broken the law protecting candidates during election campaigns from false statements.