The "black darkness of pre-Reformation popery is settling down again" across the North, the Rev Ian Paisley said yesterday.
Speaking at an Independent Orange Order demonstration in Larne, Dr Paisley said ecumenism was dangerous for the Protestant faith.
"The time is come that Protestants must expose those within their own ranks. Ecumenists are nothing more and nothing less than Rome's fifth column - their aim is to eradicate Protestantism and an easy takeover by Rome."
An agreement between the Catholic and Anglican Churches to recognise the Pope as the sole head of the Christian church showed this was the case, he said.
"Our fathers' cry is timely for this hour. No peace with Rome till Rome makes peace with God."
He accused the British government of giving in to the leaders of residents' groups on the Lower Ormeau Road in Belfast and on the Garvaghy Road in Portadown.
He also criticised the "sinister legislation coming out of the European Union which will force Christian organisations, Christian churches, educational establishments and schools to employ homosexuals, lesbians, atheists and unbelievers of every kind."