The demonstration was the latest action in a long-running dispute between Newport-based RF Brookes, which makes ready meals for M&S, and the Bakers, Food and Allied Workers Union (BFAWU).
The union staged a 48-hour strike at the factory at the start of June.
The BFAWU had previously said some of its members would lose money after changes to contracts allegedly brought about by the introduction of the National Living Wage (NLW). It claimed workers would lose thousands of pounds in shift allowances if the new terms came into force.
It was also in dispute with 2 Sisters’ Pennine Food factory in Sheffield over new employee contracts, staging two 48-hour walkouts in May and June.
However, a spokesman for 2 Sisters Food Group said connecting new terms to the NLW would be “totally inaccurate and misleading”.
He said the “majority of the 934 colleagues” at the site would receive pay increases as a result of the new packages offered.
The spokesman added: “Negotiations are all part of standard annual talks we have with unions at all our sites over the UK – Rogerstone is no different.”
Gary Johnston, organising regional secretary of the BFAWU, told FoodManufacture.co.uk that staff were not prepared to do nothing and watch their standard of living being reduced by the “greed for profits”.
He added: “It is time for a proper debate in this country for us to have a fair price for our food. All too often, supermarkets are trying to get the cheapest price to increase their profits, but it comes at a cost to those making the product.”
Erosion of rights
Cardiff Trades Union president Katrine Williams said an erosion of workers’ employment rights by successive governments had “enabled employers to mitigate the introduction of the NLW by cutting pay in other areas like shift allowances and unsocial hour payments”.
“We have found that this is becoming an increasing problem,” she added.
Last month, Unite staged a protest outside 2 Sisters’ headquarters in West Bromwich over what the union called “a number of grievances, in relation to dignity at work and impartiality practices”.
In May, Unite balloted for action at 2 Sisters’ Pizza Factory in Nottingham over possible strike action in a dispute over an outstanding pay claim for 2015.
Meanwhile, a separate BFAWU protest outside an M&S store took place on Saturday. The protest, in Leicester, was in response to allegations that Samworth Brothers had sent a ‘bullying’ letter to its employees.