MP for Liverpool Riverside Kim Johnson has said that Keir Starmer "has no b***s" during a speech on dock workers picket line.
Dock workers in Liverpool are currently on strike for two weeks over pay and conditions. Peel Ports group, which operates the port, says workers have rejected an offer of an eight per cent pay rise.
The MP joined the picket line outside Mersey Docks and Harbour Company in Seaforth.
Ms Johnson said: "I'm proud to have been elected as a Labour MP. I'm a socialist MP. I'm a member of the socialist campaign group and I bring solidarity and support.
"I will tell you that Keir Starmer will not stop me from being on a picket line."
She added: "Keir Starmer's got no b***s. We are the Labour Party, we were born out of the trade union movement and he needs to remember that."
We have asked Keir Starmer office and the Labour Party to respond to Kim Johnson's criticism and the insulting language she has chosen to use.
The docks strike is expected to continue until 3 October. Further action is possible if an agreement cannot be reached.
David Huck, the port's chief operating officer, said: "I am deeply disappointed Unite has rejected our significant pay package after many months of negotiation."
Keir Starmer has previously said Labour MPs should not be on picket lines if they want to be in government to help those struggling with the cost of living crisis.
He said, "you can't sit around the cabinet table and then go to a picket line" in some of his most direct criticism of his own MPs defying party orders by appearing at strikes recently.
He said, "I want to be prime minister of the country. I want to see a Labour government."
Sir Keir said he has "nothing against Labour MPs and others expressing their support.
On 27 July, Labour MP Sam Tarry, MP for Ilford South was sacked as Shadow Transport Minister after giving a TV interview on the picket line during a rail strike.