Union leaders are calling for a shareholder vote at Marks & Spencer to address a “structural pattern of discrimination” in the high street retailer's British supply chain.

Unite, Britain's biggest trade union, is canvassing investors to support the call for a special resolution at M&S's annual meeting in July.

It claims that, despite months of talks, nothing has been done to eradicate a “two-tier” workforce across poultry and meat suppliers. It argues that suppliers are using agency workers on a near-permanent basis, but refusing such workers, often migrants, the same conditions as full-time staff.

M&S, which was widely expected to report £1 billion in full-year pre-tax profits today, says that its suppliers meet all national standards and that many staff are paid higher rates than elsewhere in the industry. Sir Stuart Rose, the chief executive, has hailed the progress made by the retailer on ethical grounds since launching Plan A, a 100-point environmental programme, a year ago.

However, Tony Woodley, Unite's joint general secretary, said that it was time to put “warm words into action ... Our belief is that there is a structural pattern of discrimination in the M&S supply chain and this is not only ethically wrong but also presents a grave reputational risk to the brand of M&S.

“We have raised this issue time and again with M&S, but they are failing to take effective action. We are calling for an urgent meeting with Sir Stuart Rose to discuss the union's concerns.”

Unite's call comes a week after it emerged that PIRC, the corporate governance body, was seeking a special resolution at the M&S AGM over Sir Stuart's promotion to the dual role of executive chairman in July.

Shareholders accounting for more than 5 per cent of M&S stock must back a resolution for it to be put to a vote at the annual meeting. A Unite spokesman said the union was confident that its motion would be put forward.

M&S is expected to update analysts in today's annual results about the cost pressures facing the business. While the retailer is forecast to announce its best performance for a decade, analysts believe that profits could fall as low as £850million in 2008-09 as consumers cut back. Lehman Brothers believes that like-for-like clothing sales at M&S could fall by as much as 5 per cent in 2008-09.

Anne Critchlow, an analyst for Société Générale, said that it might take until 2014 for M&S to achieve pre-tax profits of £1 billion again.

M&S reported its first fall in sales for 2 years in January in a trading update that wiped more than £1.6 billion off its market capitalisation.

Sir Stuart fears that the present consumer downturn could last until 2010, but he insists that M&S is in a better position than many to weather the storm.

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