The Supreme Court has upheld a law that prohibits Americans from supporting foreign terrorist groups, even when aid is intended to turn groups toward peaceful practices.

In a 6-3 ruling, justices rejected the challenge to the federal law banning "material support" to foreign terrorists organizations -- which includes anything from technical support to legal advice.

"Even seemingly benign support bolsters terrorist activities," the justices said in the ruling.

Humanitarian groups behind the lawsuit claimed the law violates freedom of speech rights. They feared provisions in the law would put them at risk of being prosecuted for talking to terrorist organizations about nonviolent activities.

David Cole, the Georgetown law professor who represented the aid groups, said the court essentially ruled that "the First Amendment permits the government to make human rights advocacy and peacemaking a crime."

The Obama administration supports the law and calls the ban an "important terror-fighting tool."