Paul Williams has lived in Pennsylvania all his life. Yet with pretrial proceedings that begin today, Canadian libel laws now threaten to ruin him financially. Williams is a National Book Award-winning writer whose 2006 ￩xpos￩, “The Dunces of Doomsday,” revealed potential terrorist threats to the United States emanating from McMaster University in Ontario, Canada. Although the book was published only in the U.S., he’s being sued for libel in Canada by the university, which is demanding an apology and $2 million in damages. Williams is just the latest entry on an increasingly long list of victims of “libel tourism” – a list that includes me.

In this chilling assault on American free speech, “libel tourists” use foreign laws and courts, which lack America’s robust First Amendment protections, to try to silence American authors and force them into financial ruin. Congress has the power to stop this dangerous tide, if it acts now. Williams’ reporting centered on the penetration of McMaster’s College of Engineering by alleged Al Qaeda operatives. When the suspected terrorists left the school in 2004, 180 pounds of nuclear waste went missing. The U.S. government issued a “be-on-the-lookout” order and posted a reward of $5 million for each suspect.

Yet for daring to write about the threat, Williams is now being sued across the border. And Canadian libel laws are notoriously plaintiff-friendly. The same is true in Brazil, where Joseph Sharkey, a New Jersey-based freelance business columnist, is being sued for reporting about the aftermath of a plane crash he survived over the Amazon. The plaintiff is a woman who maintains Sharkey offended the “dignity” of Brazil by criticizing its incompetent air-traffic control. She is demanding $500,000 and a series of international apologies. Sharkey is likely to be convicted.

In 2005, Saudi billionaire Khalid bin Mahfouz sued me for libel in London; in a heavily researched book, I had alleged that he funded Al Qaeda. Mahfouz was a one-man wrecking crew of Americans’ free speech rights, who after 9/11 sued or threatened to sue dozens of American writers in plaintiff-friendly English courts. When Mahfouz came after me, I refused to acknowledge the British court, asserting my rights as a U.S. citizen. Nevertheless I was rendered a judgment by default and ordered to pay Mahfouz more than $250,000 and destroy the book. We must stop this assault on free speech.

Fortunately for Williams, Pennsylvania is represented by U.S. Sen. Arlen Specter, who wrote and introduced the Free Speech Protection Act of 2009. The bill would protect American writers and publishers from foreign libel judgments rendered in countries lacking America’s free speech protections. New York was the first state to pass an anti-libel tourism law, with similar laws following in Florida and Illinois.

But these patchwork protections don’t do nearly enough. Congress needs to intervene. Specter’s bill, co-sponsored by Sens. Joseph Lieberman (I-Conn.), Chuck Schumer (D-N.Y.) and Ron Wyden (D-Ore.), is now idling in the Judiciary Committee. President Obama should urge its immediate passage – before more American journalists are silenced by foreign courts.

Ehrenfeld, author of “Funding Evil: How Terrorism is Financed – and How to Stop It,” is director of the American Center for Democracy.