A federal judge is blocking legislation authorizing the government to indefinitely detain without trial an “individual who was part of or substantially supported” groups “engaged in hostilities against the United States or its coalition partners.”

Tuesday’s decision by a New York federal judge halts a key terror-fighting feature of the 2011 National Defense Authorization Act and is a blow to the Obama administration. The government urged U.S. District Judge Katherine B. Forrest not to adopt a nationwide ban on the measure, saying the move would be “extraordinary” and “unwarranted” (.pdf).

But the judge, ruling in a case brought by journalists and political activists, said the law was too vague and did not provide clear guidance on whom the government could indefinitely detain.

Last month when Judge Forrest granted standing to the plaintiffs based on their fears of being detained for their writing and political activism, she wrote (.pdf) that, “Before anyone should be subjected to the possibility of indefinite military detention, the Due Process Clause of the Fifth Amendment requires that individuals be able to understand what conduct might cause him or her to run afoul of” the statute.