Donald Trump’s executive order imposing sanctions on the international criminal court (ICC) is facing a legal challenge from two US human rights advocates who argue it is “unconstitutional and unlawful”.

In a lawsuit filed in federal court on Friday, the advocates said the order had forced them to stop assisting and engaging with the ICC out of fear the US government would punish them with criminal prosecution and civil fines.

Lawyers for the American Civil Liberties Union (ACLU), which filed the case on the advocates’ behalf, argued that Trump’s order violated the first amendment by prohibiting their constitutionally protected rights to share information with the ICC’s chief prosecutor and his staff.

They said the plaintiffs “wish to continue communicating with the [prosecutor’s office], but are chilled from doing so because of the substantial risk that they will be penalised”.