GMB warns Labour MPs that cap on political donations could endanger party funding

In its letter to MPs, the union said ‘this amendment risks having significant unintended consequences’, Photograph: Adrian Dennis/AFP/Getty Images

One of Britain’s biggest trade unions has told Labour MPs not to vote for a cap on political donations next week, saying it could endanger union funding for the party.

The GMB union has written to its affiliated MPs urging them not to vote for amendments to the representation of the people bill that would cap donations at either £100,000 or £1m.