The opposition leader said: “You can’t be in Government around the Cabinet table and then go to a picket line.”
Sir Keir made the comment with more train and Tube strikes planned for later this w
This has prompted criticism from unions, with some arguing Sir Keir’s stance contradicts the Labour Party’s original values.
A spokesperson for ASLEF told NationalWorld: “The Labour Party was forged in the labour movement.
“It’s a really odd suggestion for any Labour Party leader to suggest that a Labour MP should not attend a picket line or support industrial action by hard-pressed working people… during a cost of living crisis.”
Several Labour MPs have also demonstrated their defiance by attending picket lines, and in doing so have risked disciplinary action.
Amongst those showing support for striking rail workers was Labour MP Lisa Nandy, who earlier this month attended a picket line in her constituency Wigan.
A spokesperson for the Shadow Levelling Up Secretary said she attended to “show her support for people campaigning for better pay and conditions at a really tough time,” adding that Sir Keir had been made aware of her plans.
Carl Webb, North West regional secretary of the Communication Workers Union, thanked Ms Nandy on Twitter for her “solidarity”.
The Guardian also reported that frontbenchers Imran Hussain, shadow employment minister, and Navendu Mishra, Labour whip, also visited CWU picket lines - in Bradford and Stockport respectively.
No disciplinary action has reportedly been taken yet.
This comes after Sir Keir sacked shadow transport minister Sam Tarry following his appearance at a picket line at Euston Station in London, where the MP also gave broadcast interviews.
The Labour leader said he fired Mr Tarry for attending a media programme “without permission” and making up policy “on the hoof”.
Sir Keir recently told ITV’s Good Morning Britain that he “absolutely supports the right to strike”, but that he wants the Labour Party “not to be in Opposition but to be in Government.”
He explained: “The single most significant thing we could do for everybody who is struggling to make ends meet, whether they’re on strike or not, is to have a Labour Government.
“If you’re in Government, your job is to resolve issues, to get around the table.”
The Holborn and St Pancras MP echoed these sentiments in an article he wrote for the Mirror, commenting that he “completely understand[s] why people are going on strike to secure better pay and better conditions,” but that his focus is on transforming Labour from “a party of protest into a party that can win power.”
Why are rail workers striking?
Workers are striking as part of a long-running row over pay and conditions.
Aslef members voted to take action after the union said the firms failed to make a pay offer to help members keep pace with the increase in the cost of living.
The RMT is also in disputes over pay, jobs and conditions, and members are continuing strikes after a “paltry” offer made by transport company Network Rail.
Members of the RMT, TSSA and Unite will hold two days of industrial action on Thursday 18 August and Saturday 20 August.
These strikes will involve 40,000 staff across Network Rail and affect 14 train operators.
A separate strike by staff of TfL’s London Underground and Overground is planned for Friday 19 August, and more than 1,600 London bus drivers are also due to strike on the same day.