The Pubs Code Adjudicator Paul Newby and the deputy Fiona Dickie are launching their first investigation into Star Pubs & Bars, which is part of the Heineken Group.
The adjudicators say have "reasonable grounds" to suspect that Star has failed to comply with the pubs code by using "unreasonable stocking terms" when relationships with pubs changes.
This is reference to when pubs tenants with a "tied lease" change their arrangements and move to "market rent only" tenancies.
Ms Dickie said: "Where tenants of a brewer business regulated by the pubs code exercise their right to ask to go free-of-tie they may still be required to stock that brewer’s beer or cider within limits set out under the Pubs Code. This investigation concerns whether Star has been going beyond those limits by offering non-compliant terms".
The deadline for submission of evidence is 5pm on 7 August and the adjudicator wants to know if tenants were only allowed to stock Heineken keg beer and any other requirement to stock an "unreasonably high proportion" of Heineken brands or brands in which Heineken has a commercial interest.