Farm minister George Eustice has called on meat processors and supermarkets to show support for the beef sector’s voluntary code.
At a processor conference last week, Mr Eustice urged abattoirs to sign up to the rules to boost transparency and openness if they had not already.
Dawn Meats and Dunbia are the two biggest firms not committed to the code.
A recent NFU report also found farmers still faced a confusing lack of clarity when selling cattle direct.
In a statement after his speech, Mr Eustice said the processor code of practice, which launched in February, could bring increased transparency and efficiency to the beef supply chain.
“It will only work if processors make a commitment to their suppliers by signing up,” Mr Eustice said.
“A number of processors have already joined and I want to see more businesses commit to the code and retailers giving it their support.”
The voluntary guidelines were the main outcome from last July’s beef crisis summit, held after finished cattle prices collapsed.
The British Meat Processors Association and the NFU worked on details until the code was finally launched earlier this year.
According to the guidelines, processors are supposed to the make their terms and conditions of trading open to both current and prospective suppliers.
Abattoirs are also supposed to give farmers at least 12 weeks’ notice of any changes.
NFU livestock board chairman Charles Sercombe told Farmers Weekly last month there was still a “counterproductive” lack of openness in the processing industry.
“If they want to build up long-term relationships with their farmer-suppliers, it has to be built on transparency and trust,” he said.