The town hall’s promise to sack companies indulging in the “immoral practice” of illegal blacklisting is set to come into force today.

Unless it is called in before 5pm, Islington Council’s plan to rip up any deals they have with contractors caught blacklisting– using secret files to keep union members or safety whistleblowers out of work – will go ahead, while any companies with a history of the practice will have to prove they have now stopped and remedied their past wrongs.

The idea was first put forward by a scrutiny committee in December, but was formally adopted by a meeting of the council’s ruling executive on Thursday.

Cllr Andy Hull, Islington Council’s executive member for finance and performance said: “Blacklisting is an immoral practice that has unfairly caused huge suffering for many workers and their families.

“We’ve made it clear that we won’t work with firms who blacklist now, nor with any firms who have blacklisted in the past and can’t prove they have stopped and made amends.

“We are making a stand against an unfair employment practice that has ruined too many lives and we are challenging the government to hold a public enquiry into this malpractice, which has been widespread.”

Blacklisting is illegal and denies jobs to workers on the basis of often inaccurate information about their union and political activities.

Many workers have been blacklisted for raising completely reasonable health and safety concerns.

A national scandal about the practice erupted after a raid in 2009, where more than 3,200 workers were found to be blacklisted in the UK by more than 40 companies.

Now Cllr Richard Watts, leader of Islington Council, will write to the Government to call for a public enquiry into blacklisting, and also urge all London councils to follow their lead.

Maria Ludkin, union GMB’s national officer for legal and corporate affairs, said: “GMB welcome this kind of robust governance from local authorities.

“It is the only effective guarantee that blacklisting will be stamped out, and workers who were blacklisted compensated, by companies seeking public sector contracts.”