The coalition, which consists of various farming unions and dairy groups, also called for further increases in the milk price as a matter of urgency to help farmers struggling with spiralling costs this winter.
Farmers for Action chairman David Handley said despite all the efforts of the SOS Dairy campaign farmgate milk prices for deliveries in January were typically only 1-2p/litre higher than in April 2012. However, since then costs of production have risen by 3-4p/litre.
Mr Handley said: "Farmers need to see improving dairy market conditions translated into farmgate milk price rises."
NFU dairy board chairman Mansel Raymond said: "If co-ops, smaller processors or any milk buyer for that matter thinks the code doesn't apply to them, they are wrong.
"It is the responsibility of every milk buyer to ensure the voluntary approach to improving milk contracts succeeds. The alternative is legislation and the coalition will not rest until we see better more balanced contracts for dairy farmers."
