Marks & Spencer has been accused of misleading shoppers about the ingredients in its own-brand loaves.
The Real Bread Campaign claimed it had forced M&S into a review of its marketing and labelling after making complaints to Trading Standards earlier this year.
The retailer said it "continually work[s] ... to ensure our labelling is clear for our customers".
The campaign group took issue with several claims including the assurance that one of its white sliced loaves only contained four ingredients when it actually had 11. A sunflower and spelt loaf featured a claim on front of the packet that it had six ingredients when it fact it had 13.
The group also challenged M&S for claiming that bags of flour aimed at home bakers were made from "an ancient variety of wheat" when the flour was in fact made from a modern variety of rye.
Chris Young, the coordinator of the Real Bread Campaign, claimed that such assertions were "clearly factually incorrect" and added: "We want companies to be open and honest in their marketing and we want the Government to ensure that companies are open and honest."
A spokesman for M&S said: "All our packaging is legally compliant and we continually work with our primary authority to ensure our labelling is clear for our customers.
"Our Only Ingredients range has been created for customers who are looking for products with fewer ingredients and we're thrilled with the positive response we have seen from customers.
"We develop all our foods using processes as close to the kitchen as possible and with ingredients you'd typically find on your cupboard shelves. This approach contributes to the high-quality customers expect from M&S."
The row comes as the retailer substantially scales up its food offerings across the country. M&S is in the midst of opening six new food halls in London while renovating and expanding an existing seven sites.
The work will add over 70,000sq ft to the retailer's London space, including larger bakeries.
At the same time, M&S is opening food halls in 12 former Homebase sites across the south of England. These will be their biggest food halls to date. Its food hall in Godalming, Surrey, will be 22,000sq ft and is set to open by mid-2026.
The Real Bread Campaign has raised similar grievances in the past, including taking issue with M&S's allegedly false claim that its bread is "freshly baked in store".
The campaign claims that all M&S bread is in fact manufactured elsewhere and merely reheated in store using what Mr Young called "loaf tanning salons".