A meeting in Dublin at the weekend of the International Centre for Trade Union Rights was told that the constitutional right to union membership had no legislative support.
Mr Des Geraghty, the SIPTU vice-president, said an employer like Ryanair could unilaterally reject its employees' right to representation of their choice.
He added that Ryanair could with impunity reject the appeals of the Dail, Government, Ministers, the Labour Court, the Labour Relations Commission or the employer organisations.
Mr Michael O'Reilly, general secretary of the ATGWU, criticised the Irish Congress of Trade Unions for accepting the 1990 Industrial Relations Act. Unless the law was amended, he said, the unions should pull out of Partnership 2000.
Mr Pat Rabbitte TD also criticised the 1990 legislation which, he said, represented a decisive shift in power to employers.
He said the trade unions were now reaping the whirlwind for accepting the legislation, which was not as reactionary as that introduced in Britain during the Thatcher era but was "far more subtle".