Brexiteer Nigel Farage said the European Parliament has summoned him to explain allegations he did not declare gifts from a British insurance tycoon.
Channel 4 News published an article claiming Arron Banks had paid £450,000 (€507,221) to fund a "lavish lifestyle" for Farage after the Brexit referendum in 2016.
Farage, who could face disciplinary action from the European Parliament if he is found not to have declared the funding, said he was given 24 hours' notice to "answer allegations picked up from press stories".
He denies receiving any private money for political purposes.
A spokesman for Banks had confirmed to the BBC the gift amount and its use, adding it had been an "honour to help".
The European Parliament's code of conduct dictates that MEPs must declare gifts they've received "when representing Parliament in an official capacity" and "such gifts are reported in the register of gifts".
In a statement seen by Euronews Brussels' correspondent Jack Parrock, Farage refused to appear in Brussels on such short notice calling it a "kangaroo court".
"I did not receive any private money for political purposes. This committee would better spend its time investigating the waste of public money by well-known MEPs."
Farage's Brexit Party was the winner of the European elections in the UK and is set to fill 29 seats in the next parliament.