The US government will soon propose rules to bar meatpackers from unfairly favouring big cattle feedlots and to give poultry producers more leverage, two small-farm groups said.

The proposal would modify Agriculture Department guidelines on fair play in livestock and poultry sales. Activists say farmers are out-muscled by big packers who dominate meat processing. The 2008 farm law required action on the issue.

Two farmer advocacy groups identified the proposals as dealing with "undue preference" in livestock purchases by meatpackers and clarifying the contractual rights of producers who feed poultry for large processors.

Most US poultry, pork and beef are produced under contract to companies such as Tyson Foods Inc., Cargill, JBS USA, National Beef Packing Co. and Smithfield Foods Inc.

Producers say they have limited recourse if packers treat them unfairly. Meat processors say existing antitrust and competition laws are effective.

Agriculture Secretary Tom Vilsack said changes to marketing rules would be proposed in June but did not specify them.

Under the 2008 farm law, USDA is required to issue regulations to prevent packers from price discrimination in buying livestock. However, farm activists say small and medium-size producers do not get as good a price as big producers.