Farmers are suffering from "abuses of power" by others involved in getting their produce into shops, the NFU conference will hear.
Tim Bennett is expected to renew calls for a tighter statutory code of practice to regulate the sector.
He will tell the conference that increased costs caused by energy price rises, wages or regulation should not be passed on to food producers. Mr Bennett's speech will launch the two-day gathering at which Environment Secretary Margaret Beckett and European Trade Commissioner Peter Mandelson are also due to speak.
The conference will culminate with the results of the hotly-contested election for the post of NFU president.
Opening the conference this morning, Mr Bennett is set to say: "The NFU is not anti-business or anti-supermarket. We want a supply chain where everyone who adds value has the chance to make a profit.
"The NFU has worked manfully to find solutions, but we have been rebuffed. And the option left is an inquiry into the abuse of power and a tighter statutory code of practice."
Mr Bennett's call for the retailers' code of practice to be stricter forms part of his election manifesto.
The defending president has been challenged for the two-year post by David Handley of the Better NFU pressure group.
Mr Bennett's deputy, Peter Kendall, has also entered contest to be president.
The Better NFU as launched in December amid accusations that the NFU had failed to defend farmers' interests to Government and supermarkets. The NFU's 80 elected members will vote for the next president and vice president at a closed meeting after the conference finishes tomorrow afternoon. ..SUPL: