Mover Mark Pendlington said those on the list included people who had raised concerns over health and safety; ordinary trade unionists; and even those guilty of nothing more than raising an employment tribunal claim.

The motion highlighted how only eight of the 44 construction firms that signed up to the blacklist have agreed to work on compensation packages for those affected.

Some local authorities and the Welsh government have already taken action to encourage responsible procurement by challenging contractors. “So should we,” said Pendlington, highlighting the union’s own commitment to responsible procurement via the Prospect Pledge.

Conference was urged to maintain pressure on contractors where possible by lobbying their own employers to boycott those firms that signed up to the register.