'Broadband provider AAISP UK has complained about BT Openreach engineers showing apparent bias towards BT Retail products and services.
Adrian Kennard, Director of the service provider - which uses BT's wholesale network - explained that BT's Retail and Openreach arms are meant to be independent of each other.
But he accused the firm of trying to sell its own products and services to AAISP customers while attempting to fix their connections, reports ISPreview.co.uk.
And Mr Kennard explained that BT is paid by AAISP to fix technical issues with its network.
"When something breaks, we often have to get a BT engineer out to fix it, as they have an exclusive right to work on the national infrastructure that is the BT network," he said.
"They sometimes refer to [our] service as Infinity and have even been known to refuse to install a service because a customer does not have a BT Home Hub."
He described this as a "very anti-competitive" tactic which makes his own company - which provides services over BT's network - look "stupid".