The former culture secretary had pledged to resign from her Mid Bedfordshire seat with immediate effect in early June when Boris Johnson stood down as an MP and she failed to secure a peerage.
But she has still not done so ten weeks on, despite two councils in her constituency calling for her to step down over the lack of representation for residents.
Asked about it on LBC on Tuesday, Labour leader Keir Starmer said: “I think she should just go. I have been in Mid Bedfordshire talking to some of her constituents."
He added: “But she said she would resign with immediate effect. I don’t know what her dictionary definition of immediate effect is, but 10 weeks after the event doesn’t seem to be immediate effect.
“She has got to go, give Mid Bedfordshire an MP who will actually stand up for them, fight for them, because at the moment she is absolutely absent.
“I would say to Rishi Sunak, get a grip of this. This is one of your MPs, do something about it, force the issue and get on with it.”
Ms Dorries faces growing pressure to finally hand in her resignation, with a local council noting on Monday that she has not spoken in the Commons since June 7 last year.
In a letter, Shefford Town Council in Ms Dorries’s constituency, called on her to resign, accusing the MP of effectively abandoning the area.
“In your role as the acting member of parliament of Mid Bedfordshire, residents of Shefford feel that, due to your scant interest in your constituency, your aversion to attending local events or services and your lack of a maintained constituency office, the local area has been ‘abandoned’ by yourself,” said town council mayor Ken Pollard.
It comes after another town council in the seat, Flitwick Town Council, also called for Ms Dorries to stand aside, saying the area needed “effective representation now”.
Downing Street has previously admitted that it is “obviously unusual to have an MP say they will resign with immediate effect and for that not to take place.”
The MP has previously said that she is waiting to formally resign while she seeks answers from Downing Street about being passed over for a peerage.
The Standard has contacted Ms Dorries for comment.