Amnesty International has condemned the raid on head office of the Nigeria Labour Congress (NLC) in Abuja on Wednesday night.
Daily Trust had reported how masked security operatives dressed in black raided the Labour House over #EndBadGovernance protest.
Security operatives had launched crackdown campaign against protesters and sponsors of the protest since some persons started flying Russian flag.
In a statement on Thursday, Isa Sanusi, Director Amnesty International Nigeria, said: "Amnesty International strongly condemns the brazen invasion of the headquarters of Nigeria Labour Congress by a contingent of armed security personnel.
"The chilling raid last night, appears to be part of a sinister and calculated attack designed to intimidate the labour union. The raid by security personnel undermines workers' rights to organize, bargain collectively and take industrial action.
"During the lawless raid, the armed security personnel "ransacked books at the bookshop carrying all the materials into their van claiming that the materials were used to incite and organise the recent protest."
"We are deeply concerned about the safety of NLC officials. Under international human rights law and standards, trade unions cannot be targeted for their participating activities. Under international human rights law Nigeria has an obligation not only to respect the rights of trade unions but also to protect these rights from abuse."
Leadership of the union has condemned the raid, saying even under the military, such never happened.