Speaking in Parliament, Paula Sherriff called for a debate on the practices of big businesses and singled out the FTSE-100 retailer.
The Labour MP for Dewsbury said: “Marks & Spencer continues to charge a significant premium on products such as flowers in hospital shops and has failed to follow the requests to remove guilt lanes packed with unhealthy snacks by its tills.
“Now, it has refused to meet me to discuss its appalling treatment of British workers who staff its major UK depot and are kept on insecure contracts.
“It is exploiting loopholes in EU law to pay new staff less than others who are doing the same work.
“Does the Leader of the House agree that it is unacceptable for a brand that trades on its British ideals to treat its staff and customers in such an irresponsible manner?
In response, Chris Grayling MP said: “I have not looked at those details in Marks & Spencer, but every company today benefits from being a responsible employer and a responsible organisation.
“The honourable Lady has made her point very articulately.”
In response to the MP’s comments, a spokeswoman for Marks and Spencer told The Yorkshire Post: “Customers tell us they appreciate our stores in travel locations and hospitals and we work hard to keep prices competitive.
“Prices can be a little higher in these locations due to increased running costs, such as longer opening hours and higher rents.
“We met with Paula Sherriff on the subject of prices in our hospital stores in October.”
The spokeswoman said Marks & Spencer removed confectionery from the till points in all 580 of its owned stores in September.
Regarding the depot, the spokeswoman said Ms Sherriff was referring to a distribution centre in Swindon, which is operated by DHL, the logistics firm.
The spokeswoman added: “All employees at the Swindon distribution centre are employed either directly or indirectly by DHL and we have advised Paula Sherriff of this.”
The spokeswoman said the company works closely with DHL and has no concerns that it has contravened any of its standards.
Speaking to The Yorkshire Post, Ms Sherriff said Marks & Spencer came to her attention when she was looking into policies in hospital shops in the summer.
She said she was disappointed with the response from the retailer at their meeting, unlike WH Smith which was more receptive and made concessions on its policies.
After her meeting, she said she became aware of other claims about Marks & Spencer.
Ms Sherriff said: “I’m not going for M&S however I think it is important that those brands which trade on British ideals behave and act in a responsible manner.
“If I’m presented with evidence that does not support them, then as an MP I feel I have a duty to look into that.
“It is really important consumers and staff are getting the best deal.”
Ms Sherriff has made a name for herself as a campaigning force since entering Parliament in May.
The former hospital worker said one of her proudest achievements to date was pressurising WH Smith to reverse its policy of charging up to 90 per cent more for various items in its hospital stores than in its high street estate, taking advantange of captive audience.
Ms Sherriff said the policy is highly unethical and takes advantage of an often vulnerable captive audience.
She tabled an amendment to the finance bill last month which would have mandated the Government to include a demand for zero rate of VAT on tampons and other female sanitary products in EU negotiations.
The move won support from backbench Conservative MPs and threatened a rebellion.
But it failed to sway the Chancellor who announced that proceeds from the “tampon tax” would be donated to charities.