“Because I think that would be a mistake.”
Attacking a ban on members of the shadow cabinet attending picket lines, she urged Sir Keir to work closer with union leaders.
She added: “I think that was a mistake as well and, hopefully, if he listens to trade union leaders he will realise that was a mistake.”
Earlier this year the Labour leader urged members of his top team not to be seen joining those workers taking industrial action.
He warned the party needed to look like a Government in waiting and that those in Government cannot join strikes.
His remarks sparked outrage with trade unions threatening to withdraw millions of pounds of funding to the Labour Party if Sir Keir did not prove he was standing up for workers.