Maina Kiai, the UN special rapporteur on the rights to freedom of peaceful assembly and of association, said he was "appalled" to hear about the blacklisting of union members in the UK construction industry.
Speaking on a trip to London, he said: "It is crucial that strong actions be taken against the making and using of such lists as a deterrence."
More top news
The two children of murdered MP Jo Cox will unveil a coat of arms in the Houses of Parliament in a touching tribute to their mother.
Evacuated residents have expressed anger and confusion at unexpectedly being told they had to leave .
Following the Grenfell Tower fire, Thirteen Group has been checking its 20 tower blocks.