The quiet diplomacy with IRA and loyalist paramilitaries which helped bring about the Good Friday agreement - meetings, training seminars and facilitated dialogues - would now be deemed a terrorist offence.
Those who engaged with the Sunni Awakening Councils in Iraq may, it turns out, have been breaking the law.
And those who are currently supporting the Afghan or Somali governments' policies of engagement with their sworn enemies could be at risk of prosecution.
This clarification of a law first adopted in 1996 and adjusted in the 2001 Patriot Act, is a big setback for American organisations well known for their work in mediation, such as the Carter Center, the American Friends Service Committee or the Conflict Management Group.
The long arm of US justice means that it extends to all of its residents and citizens (including those living abroad, like myself) and those organisations that receive US government funding.
Click HERE for full article in BBC News, which conludes that, in other words, “Peacebuilding work, already dangerous to do and difficult to fund just got harder.”