Civil rights lawyers have filed a challenge to a section of the Patriot Act (search) that makes it illegal to provide "expert advice and assistance" to groups with alleged links to terrorists.

The federal ban is unconstitutionally vague and should be struck down, the New York-based Center for Constitutional Rights (search) argued in a motion filed Tuesday in federal court.

The motion was included in the center's current lawsuit over a 1996 law that makes it a crime to provide material support to any group designated a foreign terrorist organization.

The Patriot Act, passed after the Sept. 11, 2001, terrorist attacks, amended the definition of material support to include "expert advice and assistance."

One of the plaintiffs in the case would like to work as a doctor in his war-torn homeland of Sri Lanka. Because some hospitals are controlled by rebel forces there, he fears he could be prosecuted for "providing material support" to a terrorist group, according to the filing.

"In its rush to pass the Patriot Act just six weeks after the Sept. 11 attacks, Congress overlooked one of our most fundamental rights -- the right to express our political beliefs, especially those that are controversial," attorney Nancy Chang said in a statement.

It was the second legal challenge in less than a week to the Patriot Act, which gives the government expanded surveillance powers and has been criticized by some as infringing on civil liberties.

Last week, the American Civil Liberties Union (search) filed suit in Detroit against a provision of the act that allows federal agents to secretly monitor books people buy or check out of libraries.

The Justice Department defends the act as a crucial weapon in the war on terrorism. In the Detroit case, spokeswoman Barbara Comstock said the section targeted goes to great lengths to protect First Amendment rights and requires court approval to obtain records.