Labour's Tom Watson says Unite commerce union chief Len McCluskey is attempting "to take me out as deputy leader".
He informed the BBC's Nick Robinson the union chief was "coming for me"however he was not going to be "bullied" out of his job.
He mentioned he needed to "bring everybody back together" within the party.
Mr McCluskey has beforehand accused Mr Watson of behaving like a "low-budget remake of the Godfather" over claims of a exhausting left plot to take over Labour.
His workplace declined to touch upon Mr Watson's newest claims.
The two males had been as soon as shut buddies and even shared a flat collectivelyhowever Mr Watson mentioned they fell out in September 2016 when Jeremy Corbyn was unsuccessfully challenged for the party management by Owen Smith.
Speaking to Nick Robinson's Political Thinking podcast, Mr Watson mentioned: "It could be very tough that, as a result of we had been buddies socially in addition to understood one another politically.
"Sadly, we fell out over that week when Jeremy went into the second leadership election, and I've not spoken to him since that week."
Unite is Labour's largest and strongest commerce union affiliate and largest donor.
Mr Watson, who was elected deputy chief of the party on the identical time Mr Corbyn turned chief in September 2015, is believed to have come beneath stress to denounce Labour MPs who had backed a vote of no confidence in Mr Corbyn.
"I felt very tough there, as a result of Unite funded my marketing campaign, they did not nominate me, and I believe he felt that I, indirectly, was obligated to him personally.
"And my obligation was to the Labour Party. You might severely criticise me for taking the incorrect place, and that is truthful, however I am not going to be bullied by Len McCluskey.
"I certainly wasn't going to be bullied by Rupert Murdoch, so I'm definitely not going to be bullied by Len McCluskey. And I think he found that very difficult."
The MP, who fought a long-running battle with Mr Murdoch's newspaper group over cellphone hacking, mentioned he felt he was being persecuted by Mr McCluskey.
"Yes, he is coming for me. They're upping their delegates and all of that," he mentioned.
"What will be, will be. He's powerful enough, if he wants to take me out as deputy leader, he probably could, but that's up to him. I'm just going to get on and try and bring everybody back together and do what I can as best I can."
There isn't any formal mechanism for eradicating the Labour Party deputy chief.
But Mr Watson is known to be involved that Unite is engaged in a takeover of the party, with the appointment of Unite officers to key roles, similar to new common secretary Jennie Formby and Mr McCluskey's chief of workers, Andrew Murray, who has been seconded to the chief's workplace.
Karie Murphy, who was Unite's favoured candidate within the 2013 choice row forward of the Falkirk by-election, is Mr Corbyn's chief of workers, whereas Amy Jackson, a former Unite official, is his political secretary.
Mr Watson has additionally clashed with Mr McCluskey over the union chief's assist for the pro-Corbyn stress group Momentum and efforts by native party activists to de-select some Labour MPs.
Mr McCluskey has spoken of his unhappiness on the demise of his friendship with Mr Watson, however has additionally accused him of collaborating in "a stupid and rather sinister coup" to eliminate Mr Corbyn.
In September final yr, he known as for a feminine deputy chief to be introduced in to work alongside Mr Watson.