M&S has called for a ban on retrospective changes to suppliers' contractual terms.
The retailer said in a submission to the Competition Commission's groceries inquiry that the practice gave "rise to significant adverse effects for suppliers".
"The risk of such changes occurring is likely to hamper innovation and investment in new products," it added. The Code of Practice, to which M&S is not a signatory, permits retrospective changes to terms of trade if they are "reasonable".
M&S said it was happy for the "reasonableness test" to continue to be applied to all other practices that "do not clearly impact adversely on competition".