The Federation of Communication Services (FCS) has raised concerns over Ofcom's agreement with BT about Openreach's future.
Last week, BT agreed to the watchdog's demand for its infrastructure subsidiary to become a distinct and legally separate company.
The FCS has welcomed the announcement and said it is looking forward to working with the new legally independent Openreach and its board.
Nevertheless, the organisation believes the agreement between Ofcom and BT could have gone further.
"We believe it is the first step is in the right direction," the FCS said.
"However, we remain convinced that the only sustainable and truly customer-responsive Openreach is an Openreach which is fully master of its own destiny, structured and managed as a utility company and completely structurally separate from BT."
The FCS has been a longstanding advocate of a full structural separation of BT and Openreach and has been lobbying for it under the banner of Fix Britain's Internet, along with Three, Sky and TalkTalk.
BT's agreement with Ofcom means Openreach will be run by its newly-established board, the majority of which consists of directors independent of BT.
Openreach will also offer its own unique branding, with any traces of BT's branding removed to reflect its greater independence.
BT's decision to agree to the changes means they no longer need to be forced upon the company through regulatory intervention.
The process of carrying out the reforms will take place in the coming months.