Unite general secretary candidate Jerry Hicks told a rally of his supporters that if he was in charge the union would support the occupation of workplaces to defend jobs - even if it meant breaking the law.
He said that Unite should have supported the Vestas workers on the Isle of Wight who took over their factory last year - instead of repudiating their action to avoid having the union funds sequestrated.
Hicks said members of the union would not have noticed when "officials cars ran out of petrol" but that employers noticed when Unite failed to stand up for jobs.
He told the 60-strong meeting at the Indian YMCA in Fitzroy Square, London, on October 11,: "Employers watch what we do, they listen to what we say, and when we say nothing they come for us."
Hicks said he would take only the average wage, "not the £200,000" earned by the current joint general secretaries.
He said more officials should be elected.
Hicks added that people called him an extremist - but that employers who sacked people for organising a trade union were the real extremists.
Also speaking was film director Ken Loach - who's movies include Bread and Roses about union organisation.
He said: "Trade unions represent all that's best of our experience: mutual support; solidarity; collective action; and looking after the weak by the strong.
"Jerry Hicks represents all that's best in trade unionism."
The winner of the election will be the first solo leader of Unite - a union of more than a million members formed by the merger of Amicus and the TGWU.
Hicks's suppporters say it's a two horse race between their man and Len McCluskey who is supported by the United Left organisation.
The other candidates are Gail Cartmail and Les Bayliss.
The vote starts on October 25.