The behaviour of Unite officials in Falkirk was "amateur and irresponsible", former Labour MP for Falkirk Eric Joyce wrote in the Guardian, after reports that trade union Unite paid for votes to secure friendly candidates at the General Election.
Mr Joyce wrote: "Over the years, trade unions have used their putative power sensibly. They've understood that party rules create the possibility of serious dysfunction if they choose to overexert their potential muscle.
"In Falkirk I've found them to be a stabilising influence in partnership with the Labour party. Until now.
"The amateur, hubristic and irresponsible actions of a small number of Unite officials at the top of the organisation will require some rules to be changed to prevent another Falkirk".
Labour leader Ed Miliband has turned on the trade union Unite - his biggest financial backer - whose votes helped him become leader.
Tom Watson has announced his resignation from the shadow cabinet, amid a row about the influence of the union Unite on the Labour party.