Daniel Ray Carter Jr. logged on to Facebook and did what millions do each day: He "liked" a page by clicking the site's thumbs up icon. The problem was the page was for a candidate challenging his boss, the sheriff of Hampton, Va.

That simple mouse click, Carter says, caused the sheriff to fire him from his job as a deputy and put him at the center of an emerging First Amendment debate over the ubiquitous digital seal of approval: Is liking something on Facebook protected free speech?

Carter filed a lawsuit claiming his First Amendment rights had been violated, and his case has reached the U.S. Court of Appeals for the 4th Circuit.

This week, Facebook and the American Civil Liberties Union filed briefs supporting what they say is Carter's constitutional right to express his opinion, signaling the case's potentially precedent-setting nature.

The interest was sparked by a lower court's ruling that "liking" a page does not warrant protection because it does not involve "actual statements."

If the ruling is upheld, the ACLU and others worry, a host of Web-based, mouse-click actions, such as retweeting (hitting a button to post someone else's tweet on your Twitter account), won't be protected as free speech.