Phil Reddall, the party's North Shropshire group organiser, said it would be taking more action against the decision.
More than 70 people wrote to Shropshire Council to object to plans by the Oswestry Muslim Society to develop a 19th century former Presbyterian church on Oswald Road while more than 40 wrote in support.
The bid was approved by council officers under delegated powers. Mr Reddall said he was 'disappointed but not surprised' the decision was not taken by councillors at an open meeting.
He said: "We can't say too much about what we will doing yet but we will be taking action in Oswestry, obviously within the law."
Oswestry Muslim Society's estimated 70 members meet at Eastern Oswestry Community Centre.