Andrew Stern, president of the Service Employees International Union, on Wednesday day called on Congress to look more broadly at the “tax dodges” of private equity groups which he said are receiving billions of dollars in public subsidies “at the expense of everyone else”.

Mr Stern’s attack is significant because SEIU – one of the US’s most centrist and pragmatic unions – had this year said it wanted to work with private equity groups to ensure employees of companies taken over in leveraged buyouts were treated as stakeholders.