A source close to the MP said that there is “huge frustration” over the way Unite allegedly “blocked” efforts to appeal directly to members to vote Labour in the election in Scotland and follows ill feeling over Mr McCluskey’s role in forcing Scottish leader Jim Murphy to quit.
The row came as shadow education secretary Tristram Hunt said the party needed to consider “devo-max” for England and Scotland. He also said he was not standing for the UK Labour leadership.
The source close to Mr Murray source said: “If Len McCluskey can use his authority to decide who is the leader of the Scottish Labour party then why can’t he do the same to get his members to vote Labour in Scotland.”
A Unite spokesman said: “We are happy to meet Mr Murray and discuss the way forward.”