The Freemasons have launched legal action against the Metropolitan police after the force ruled officers must declare any links to the organisation, amid fears membership could be linked to corruption.

The United Grand Lodge of England (UGLE) has sent the Met a letter before claim, signalling its intention to seek a judicial review unless what it describes as the “unlawful, unfair and discriminatory” policy is suspended.

The decision follows the Met’s announcement that Freemasonry would join its list of “declarable associations”, requiring both serving and prospective staff to disclose membership.

The force said the move was aimed at boosting transparency and addressing concerns about “hierarchical organisations that require members to support and protect each other”.

The Met said it had surveyed its officers and staff, and that two-thirds backed the requirement for Freemasons to declare their membership because it “affects public perception of police impartiality”.

Commander Simon Messinger said last week: “After such conclusive results from our consultation, we have decided now is the right time to address longstanding concerns and that public and staff confidence must take precedence over the secrecy of any membership organisation.

“Our decision does not mean any member of staff cannot join the Freemasons or another similar organisation.”

UGLE said the change infringed members’ rights, breached equality and data protection laws, and followed a consultation process it called “wholly inadequate, prejudicial and unjust”.

Adrian Marsh, UGLE grand secretary, said the Met’s decision “casts an aura of mistrust” over the Freemason community.

He said: “Given the obvious, detrimental impact on our members, United Grand Lodge of England, Order of Women Freemasons and Honourable Fraternity of Ancient Freemasons consider that we now have no choice but to take legal action to challenge this unlawful decision.

“We do not take this decision lightly but feel that we are left with no other options, in order to defend the rights of those in our membership, both male and female, present and past, that serve the people of London loyally in any capacity under the banner of the Metropolitan police.”

The Metropolitan police have been approached for comment. (The Guardian UK)

• Freemasons at the beginning of a meeting in the Grand Lodge in Covent Garden. Photograph: Graeme Robertson/The Guardian