A Conservative MP has called for a register of interests for trade union bosses.
Rob Wilson, Reading East MP, said union chiefs were "full-time politicians in all but name" and received £113m of taxpayer funding each year, arguing that a register would subject them to the same level of public scrutiny as all other politicians.
Communities and Local Government Secretary Eric Pickles said he was "shocked" to learn that such a register did not already exist.
"I'd have thought that in this age of transparency we should be urging them to do that," he told MPs during questions to his department on 5 December 2011.
Mr Pickles had earlier called for councils to review the "merits" of publicly funded full-time union officials, telling MPs it was "wrong" that taxpayers' money should be used to subsidise trade union activity.
But several Labour MPs criticised the "attacks" on trade unionism.
Labour's John Healey said trade union representatives were the "unsung heroes of Britain's volunteering tradition" who provided day to day support for staff and cut the number of employment tribunals.
His party colleague Ian Lavery agreed, saying the work carried out by reps saved the industry and taxpayers "millions and millions of pounds".
Another Labour MP, Gerry Sutcliffe, described them as a "force for good".
Mr Pickles responded that he was "very pro trade unions" but believed that trade union activities should be carried out on a voluntary basis.