How exactly do the trade unions fund the Labour Party - and will Ed Miliband's proposed changes work?
Rewind to 1984, and the then Prime Minister Margaret Thatcher introduced the Trade Union Act.
It sets out that unions must ballot their members every ten years if they want a political fund, that is money to spend on campaigns.
Unite, the country's biggest union with 1.4 million members, held its own ballot on retaining a political fund earlier this year.
It was the first time it had had to do it, since Unite came together as an amalgamation of its predecessors, Amicus and the Transport and General Workers Union.