Sainsbury's announced a 7.3 billion pound deal to buy U.S. group Walmart's Asda in April. If it goes ahead, the combined giant will overtake Tesco as Britain's biggest supermarket group.
The competition regulator has started a preliminary probe into the deal ahead of a formal investigation, while on Wednesday MPs from the Environment, Food and Rural Affairs Committee said that they would also gather evidence on it.
"Grocery retailers do not have a great record of treating their suppliers well," the committee's chair Neil Parish said in a statement.
"My committee is holding this session to investigate how the biggest potential shake-up of the grocery market in recent years could affect British farmers and suppliers, as well as consumers."
The cross-party group will question Sainsbury's Mike Coupe and Asda's Roger Burnley on June 20.
(Reporting by Sarah Young; editing by Stephen Addison)
