The Department of State Services (DSS) has released Nigeria Labour Congress (NLC) president Joe Ajaero.
Mr Ajaero was reportedly released on bail at about 11:10 pm.
The labour leader was arrested at the Nnamdi Azikiwe International Airport in Abuja on Monday on his way to the United Kingdom for a global Trade Union Congress meeting.
NLC had given the DSS a midnight ultimatum to release Ajaero while placing its affiliates on alert.
“The congress will not stand idly by while the rights of its leaders and members are trampled upon. Accordingly, we demand for the immediate and unconditional release of Comrade Ajaero,” NLC spokesman Benson Upah said in a statement.