Regional broadcaster Six TV joins Virgin and Sky in claiming the joint venture will unfairly dominate the online TV market.
Virgin lodged an official complaint earlier this year and now Six TV has branded the venture a “poison pill” for the local TV industry.
Detractors also claim the service will place too much pressure on the UK’s struggling broadband network.
Six TV chief executive Daniel Cass said: “Some parties appear to present the Project Canvas platform as the answer to the challenges faced by new local TV services.
“Far from a panacea, we regard Project Canvas as a poison pill which will have a negative effect on opportunities for important new television services to enter the market. We are calling upon Ofcom to launch a full investigation of the actions of the joint venture partners as we do not believe local TV will be viable in the UK otherwise.”
The joint venture between media and telecoms giants including TalkTalk, BT, Arqiva, Channel 4, ITV, Orange and Channel Five aims to apply the success of Freeview to the online TV market by making it available through a set-top box.
Its members say the system is open and other firms are welcome to join the project.