Nigel Farage has been summoned to attend an EU conduct committee to be questioned over gifts he received from Arron Banks.
The committee will decide whether Mr Farage broke any European parliament rules in failing to declare the rent on a Chelsea home and expenses for a trip to the United States in 2016, which Mr Banks paid for.
The Code of Conduct for MEPs requires them to declare gifts made to them “in the performance of their duties”.
Mr Farage said the payments were not made for political purposes, and that he did not have to declare them.
The meeting will take place at 5pm on Wednesday in Brussels, but Mr Farage has said he will not attend.
If he is found guilty of any wrongdoing, the committee will make a recommendation to the European parliament president on any punishment Mr Farage should receive.
The European parliament president, Antonio Tajani, could hand down a reprimand, a financial penalty or suspend Mr Farage from certain parliamentary activities for up to 30 days.
If Mr Farage was temporarily suspended, it would be the first time any MEP received the punishment.
He would retain his parliamentary pass and be able to vote in the debating chamber, a European parliament source said.
Mr Farage has said he would not attend an “EU kangaroo court”, and that he “did not receive any private money for political purposes”.
““What is this but an EU kangaroo court where I am given 24 hours notice about allegations picked up from press stories?” he said.
“I will not be attending at such short notice.
“And if they try to bar me from the building, who else gives voice to the thousands of people who voted for me? Is this democracy EU style?
“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.”