To amend the Internal Revenue Code of 1986 to terminate the tax-exempt status of terrorist supporting organizations.

HR 6408 would amend tax law to revoke the tax-exempt status of organizations providing material support (beyond a minimal amount) to groups designated as terrorists under existing law. It directly affects nonprofit organizations that, within three years of a Treasury designation, supplied resources like funds or equipment to terrorist organizations. Key mechanisms include requiring the Treasury Secretary to send written notice to the organization before designation, granting a 90-day "cure period" to prove no support was provided or return resources, and allowing rescission of the designation if errors occur or notice was not received. The bill applies to tax years beginning after its enactment.