Trade Unions Congress (TUC) general secretary Paul Nowak visited Nautilus's head office and retirement complex at Mariners' Park, as Heart Unions Week kicked off.
Mr Nowak toured the estate and with Nautilus general secretary Mark Dickinson and director of welfare and care Andrew Jones.
The Union moved its headquarters to the Wallasey site in February 2022 and received planning permission for a new multi-million-pound redevelopment of Nautilus House.
Heart Unions Week celebrates the trade union movement which fights tirelessly for fair treatment at work, safe conditions, better wages, pensions, sick pay, annual leave, maternity and paternity rights, equality, social justice and more.
Nautilus members spoke about why they joined the union in a series of video posts.
Mr Nowak succeeded Frances O'Grady when she retired at the end of the 2022.