Frances O'Grady
Frances O'Grady, general secretary of the TUC, has written to Vince Cable urging him to relax union balloting lawsGetty

The Trades Union Congress has written to the government pleading for reform to the archaic and restrictive laws that mean workers can only be balloted on industrial action by post.

The letter to UK Business Secretary Vince Cable comes after over a million public sector workers went on strike over pay and conditions amid the government's austerity drive to cut spending.

David Cameron, the Conservative prime minister, criticised the walkouts and said he would tighten union laws by setting a 50% turnout threshold on ballots if his party wins the 2015 general election. Unions often see poor turnouts for strike ballots, which critics say means industrial action is not justified.

But the TUC is asking for unions to be allowed to ballot members electronically so they can vote on their computers or even smartphones. It said when unions use digital routes to survey members they have been known to get a response rate of as high as 96%.

"In the run up to and during last week's public sector strike much of the rhetoric coming from parts of government was about making it harder for ordinary workers to go on strike by raising the bar on the number of votes needed, with a view to either stopping lawful industrial action taking place altogether or exposing unions to claims for damages," wrote Frances O'Grady, TUC general secretary, to Cable.

"In our view this amounts to an attempt to ban strikes by the back door. The rules governing industrial action ballots in the UK are already very stringent and while there is absolutely no case for imposing a tougher turnout threshold – that not a single Westminster MP met at the last election – unions are keen to explore ways that industrial democracy could be strengthened."

Under the Trade Union and Labour Relations Act 1992, unions must write letters to members at their home addresses to ask whether or not they agree with proposed industrial action.

"This means of communication works for some, but for many workers leading busy lives, it's all too easy for the ballot envelope to be put to one side – at best only opened after the deadline or, as is more likely, simply recycled," said O'Grady.

"Whilst any strike ballot where a majority of members in a workplace vote for action is a legal and legitimate result, unions would clearly prefer to see more people participating. But to do that we need to update the rules and let people vote on their digital devices."

The TUC launched an online petition for reform of union balloting rules alongside O'Grady's letter.

"The government understands the need to modernise the way in which union ballots are held, whilst also allowing all union members to use whatever method is best for them to communicate with their union," said a spokeswoman for the Department for Business, Innovation and Skills.

"There are no current plans to change industrial action law, however we will keep any ideas under consideration."