Ukip’s ruling committee has unanimously backed a vote of no confidence in leader Henry Bolton.
Party members will now be given a vote on whether the former Army officer should remain in post.
Ahead of the meeting of Ukip’s national executive committee, Mr Bolton insisted he would not quit and said forcing him out would probably end the party.
A Ukip spokesman said: “The committee took the decision to hold a vote of no confidence in the leadership of Henry Bolton.
“The vote was carried unanimously with the exception of the leader.
“This decision will automatically trigger an emergency general meeting of the party, to allow the membership of Ukip the democratic opportunity to decide to endorse or reject that vote of no confidence.”
Under Ukip rules, an emergency general meeting must be staged within 28 days.
Members will be told about when and where it will be held in the next 10 days.
Mr Bolton faced a wave of calls to resign after his now former partner Jo Marney was revealed to have made highly offensive comments about Meghan Markle and black people.
But he refused to step down, warning that the months of in-fighting a vote of no confidence would lead to meant “that the reality is that the party is probably over”.
The under-fire leader said a contest to replace him “would be financially almost unviable for the party”.
Mr Bolton said previously his “romantic” relationship with 25-year-old model Ms Marney was over but he admitted they were “still in touch” after pictures emerged of them meeting up.
He left wife Tatiana, 42, who gave birth to their second daughter at London’s St Pancras station in 2016 after going into labour on a train, prior to his relationship with Ms Marney becoming public in early January.
Mr Bolton told ITV’s Peston On Sunday: “I don’t believe I have done anything wrong.
“My own personal life, it’s a little bit of a mess at the moment. I need to sort that out, of course.”
Asked about reports his estranged wife still did not know if their marriage was over, he replied: “My wife and I have exchanged lengthy emails on this. We have spoken a couple of times on the phone, but that is my business.”
Since the referendum, Ukip has struggled to hang on to a leader.
Diane James quit within a matter of weeks after replacing Nigel Farage.
Another election saw Paul Nuttall take the job, only to step down just seven months later.
Steve Crowther stepped in as acting leader while a fresh poll was held and Mr Bolton took over at the end of September.
Neil Hamilton, Ukip’s leader in Wales, said Mr Bolton should “seek psychological help”.
He said: “I support the NEC’s unanimous decision to pass a vote of no confidence in Henry Bolton.
“He should now resign from Ukip immediately so we can get on with rebuilding the party without further distraction.
“If he forces us to hold an EGM, he will only humiliate himself further.
“His recent behaviour has been so irrational, he should seek psychological help.
“With a calm, experienced person like Gerard Batten MEP or Mike Hookem MEP as interim leader, we can establish the party’s role in a post-Brexit Britain.
“Ukip fills a gap in the spectrum left by the failure of all the old parties to speak for the ordinary, common sense person.
“Ukip Wales is well advanced with its own plan for an enduring role in Welsh politics.”