The US arm of a UK charity under investigation by the Charity Commission for links to the Conservative Party has been referred to the US Internal Revenue Service after its chief executive appeared to back David Cameron's election campaign.
Atlantic Bridge exists to promote close relations between the US and the UK and was founded by shadow defence secretary Liam Fox. It has branches on both sides of the Atlantic.
Amanda Bowman, chief executive of Atlantic Bridge Inc, the US-based organisation, wrote an article last week for Washington DC newspaper The Examiner, in which she said that Tory leader Cameron would be "much more amenable to shared US-UK foreign interests than Gordon Brown", and that the Conservative leader would be "good for America and better for the special relationship".
After Stephen Newton, a blogger on politics and culture, complained about Bowman's article, the Charity Commission told him it had notified the IRS, which determines the tax-exempt status of non-profits in the US.
Neither the IRS nor the Charity Commission would comment on the move.
Tax-exempt charities in the US - known as 501(c)(3) organisations - are prohibited from endorsing election candidates in the US or abroad. Wilful breaches result in revocation of their tax-exempt status.
One US-based lawyer specialising in non-profit law, who asked not to be named, said: "Political activity is an absolute prohibition. Endorsing candidates or taking a position vis a vis candidates is an absolute prohibition."
But he added that US charity executives were permitted to endorse candidates in a personal capacity.
"While it seems cut and dried, you could also see their lawyer arguing that she was speaking in an individual capacity, even though the article identifies her by her job title."
In a statement, Atlantic Bridge, said: "We are confident that no aspect of the recent op-ed in question is in violation of 501(c)(3) laws."
The Charity Commission opened a regulatory compliance case in August into the UK branch of Atlantic Bridge for alleged breaches of political neutrality. The inquiry is continuing.
The two charities share an advisory council, which includes seven Tory MPs and a Tory peer.