Ukip has warned anti-racism campaigners that they face prosecution if they go ahead with a planned meeting about the party.
The Movement Against Xenophobia plans to hold a meeting titled "Stop Scapegoating Immigrants" on Monday, focusing on Ukip's "vicious and racist" campaign against immigration.
However, Ukip have written to the group complaining about the appearance of their former staffer, Jasna Badzak on the panel.
In a series of emails seen by Politics.co.uk, Ukip MEP Gerard Batten warned that the group could face prosecution under election law if they allow Badzac to make any "false accusations" against him.
Batten said he would not hesitate to take action.
"All past experience leads me to think that if [your] organisation gives her a platform she will use it to make false allegations against me," he wrote.
"If that happens then she and the organisers of the meeting could be in breach of the Representation of the People Act 1983, Section 106, 'False statements as to candidates’ during an election.' This is a criminal offence..."
"If I find that the platform has been used to make false accusations against me during this election period then I will make a formal complaint to the Metropolitan Police under the Act."
In a later email he said he would forward his correspondence with the organisation to the police.
Badzac was last year given a suspended sentence for forgery and fraud, after doctoring a bank statement to make it look like she had not been paid by the European Parliament.
She later took a loan from Batten which she failed to repay. Batten claims she is now repaying the money at the rate of £100 a month.
Badzak says her relationship with Batten deteriorated after being asked to work on a policy document titled "dismantling multiculturalism."
Batten has repeatedly caused controversy over his call for UK Muslims to sign a "code of conduct" declaring their opposition to extremism.
The Joint Council for the Welfare of Immigrants, who have organised Monday's rally insist that Badzac will not be speaking about Batten but about the racism and xenophobia she claims to have witnessed while working for Ukip.
"The purpose of our meeting is to have an open discussion that articulates the facts behind immigration and the experiences of immigrants to ensure misinformation does not go unchallenged," Legal and Policy director Saira Grant told Batten.
"We have no intention of allowing our meeting to be hijacked by personal attacks on any individuals from any side."
Green Party leader Natalie Bennett will also be appearing on the panel on Monday, alongside a representative from the National Union of Students and other anti-racism campaigners.
Batten's threat is the latest in a series of attempts by the party to secure prosecution of their critics.
Earlier this week, three Ukip MEP candidates released a statement warning that they would prosecute anybody calling them "fascists" at an upcoming meeting.
They believe that any allegation of fascism amounts to a "hate crime" which should be prosecuted.
A blogger who posted a tweet criticising Ukip policies was also visited by police after a complaint from the party and asked to remove the tweet.
Cambridgeshire Police have since apologised for the incident.
"I believe in this instance police attendance was not required and I have asked for our approach to this sort of incident to be reviewed to ensure we do not get involved unless there is clear evidence that an offence may have been committed," chief constable Simon Parr said in a statement.