Only 38 MPs would have been able to take up their seats in Parliament under balloting restrictions on unions being called for by business leaders, according to a new study.
The CBI has been pressing ministers to change the law so that 40% of union members balloted would have to support a walkout before it could go ahead, while London Mayor Boris Johnson believes at least 50% of those balloted should vote.
Research by Labour MP John McDonnell (Hayes and Harlington) showed that if the same criteria was used during a general election, the Commons would be left with just 38 MPs who won the support of 40% or more of the total electorate in their constituencies, with those losing out including Deputy Prime Minister Nick Clegg and Chancellor George Osborne.
The report was published ahead of a lobby of Parliament by union activists in support of a Private Members Bill by Mr McDonnell aimed at ruling out "frivolous" attempts by employers to overturn industrial action ballots in the courts on minor technicalities.
Mr McDonnell said: "MPs and the Mayor of London should not require trade unions to pass a greater democratic test than they themselves have achieved. All trade unions want is to be treated fairly and to have their members' democratic decisions respected."
Bob Crow, leader of the Rail Maritime and Transport union, said: "We know that there has been a new push from the bosses organisations, the Mayor of London and other Tory politicians since the election to try and get the Government to load the law on industrial action even further in their favour. This research shows that as far as they are concerned it's one version of democracy for the political class and another for the working class."
Mark Serwotka, general secretary of the Public and Commercial Services union, said: "The UK already has the most restrictive trade union laws in Europe. No one can take seriously proposals from the CBI which if applied to Parliament would exclude 94% of MPs or proposals from the London Mayor that would make his election invalid."