The U.S. Supreme Court on Monday upheld the federal law criminalizing “material support” for designated terrorist groups (pdf), rejecting complaints that the law is so vague that it would stifle political speech by groups with peaceful intent.

The 6-3 decision was a major victory for government prosecutors, who frequently use the statute as a weapon to neutralize individuals with suspected ties to terrorist groups. In most war-on-terror cases the Supreme Court has ruled on since the Sept. 11, 2001, attacks, the government has not fared nearly as well. The decision may also be a boost for Solicitor General Elena Kagan, who defended the statute at oral argument Feb. 23. Her Senate confirmation hearing for a seat on the Supreme Court begins on June 28.