The U.S. Supreme Court on Monday revived a challenge by two conservative groups that contend an Ohio law imposing fines for making knowingly false statements about political candidates violates their right to free speech.

The court voted 9-0 that the lawsuit could go ahead even though the Ohio Elections Commission had not said whether it would pursue an enforcement action against the Susan B. Anthony List and the Coalition Opposed to Additional Spending and Taxes (COAST).

The groups said the possibility that they could face sanctions deterred them from issuing statements during the 2010 election campaign criticizing Democratic congressman Steven Driehaus.

Susan B. Anthony List wanted to put up a billboard criticizing Driehaus for supporting the 2010 Affordable Care Act, often called Obamacare.

Justice Clarence Thomas wrote on behalf of the court that the groups had standing to sue in part because of the possibility of free speech being suppressed.

"The burdens that commission proceedings can impose on electoral speech are of particular concern here," Thomas wrote.

The state's lawyers say the groups could show neither that the law threatened their free speech rights guaranteed by the First Amendment to the U.S. Constitution nor that the commission was likely to prosecute them.

Driehaus, at the time a U.S. congressman from the Cincinnati area, had filed a complaint with the commission concerning Susan B. Anthony List, which opposes legalized abortion. Driehaus lost his re-election bid and the complaint was withdrawn.

The Ohio law makes it a criminal offense to make knowingly or reckless false statements about a candidate. The maximum penalty is a fine of $5,000 and six months in prison, according to lawyers for the groups.

COAST joined the legal battle, although it had not been the subject of a complaint.

A federal judge in Ohio dismissed the two groups' challenge to the law in August 2011. The Cincinnati-based 6th U.S. Circuit Court of Appeals upheld that decision in May 2013.