Voluntary rules are useless at stopping retailers abusing their power, say agriculture committee MEPs.
They are calling for legislation to combat unfair trading practices in the food supply chain, where farmers always come off worst.
In an opinion that will feed into a non-binding resolution, agriculture committee MEPs have called for the introduction of European Union legislation "without delay".
And the legislation should include sanctions, they say.
It's the only way to protect farms from unfair trading practices such as late payments, arbitrary discounts and retroactive contract changes.
"Across the political groups in the committee there is a clear demand for Commission action," said rapporteur Mairead McGuinness, after the opinion was adopted by 39 votes in favour, with two abstentions.
The agriculture committee opinion will be part of an Internal Market and Consumer Protection report to be voted by the whole House in January or February.
European Commission farms chief Phil Hogan has repeatedly said ensuring fairness in the supply chain is one of his top priorities. Brussels is currently analysing market structures and their impact on farm-gate prices.
Spain introduced it's own food-chain legislation in 2013 and it has been hailed a model for European Union-wide legislation. Britain's Groceries Code Adjudicator has also attracted favourable comment.