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 that the page was for a candidate who was 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 that 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 re-tweeting (hitting a button to post someone else's tweet on your Twitter account), won't be protected as free speech.

"We think it's important as new technologies emerge . . . that the First Amendment is interpreted to protect those new ways of communicating," said Rebecca K. Glenberg, legal director of the ACLU of Virginia. "Pressing a 'like' button is analogous to other forms of speech, such as putting a button on your shirt with a candidate's name on it."

Facebook's like button appears next to many different types of content on the site, from photos of a friend's kids to an organization's page to news articles. When someone clicks the button, an announcement is posted on his or her profile saying that the user likes that piece of content. The like is usually displayed to the user's Facebook friends as well. Facebook says there are more than 3 billion likes and comments registered every day.

The like controversy is just one of many thorny issues surrounding social media in the workplace.

In April, the Marine Corps said it would discharge a sergeant who criticized President Barack Obama on his Facebook page — including allegedly putting the president's face on a poster for the movie "Jackass." And last fall, the National Labor Relations Board ruled that a New York nonprofit illegally fired five workers who criticized a colleague on the site.

The board, a federal agency that brings labor-related complaints on behalf of workers, said it had seen the number of cases involving social media skyrocket from zero to more than 100 over five years.

Carter's troubles began in the summer of 2009, when longtime Hampton Sheriff B.J. Roberts was running for reelection, according to the lawsuit, filed in federal court in Newport News, Va. in March 2011. Roberts learned that some of his employees, including Carter, were actively supporting another high-ranking Sheriff's Office official, Jim Adams, in the election.

Carter liked Adams's election page on Facebook, according to court records. When Roberts learned of the campaigning on the site, he became "incensed" and called a meeting of employees, according to the lawsuit. He allegedly told them that he would be sheriff for "as long as I want it."

After the meeting, the lawsuit says, Roberts approached Carter and told him: "You made your bed, now you're going to lie in it — after the election you're gone."

About a month after Roberts was reelected, Carter and five other employees who supported Adams or did not actively campaign for Roberts were fired, according to the lawsuit. The other employees are also parties in the lawsuit. Carter and his attorneys did not return calls for comment.

In filings in response to the suit, Roberts's attorney disputes Carter's version of events and says the firings were not politically motivated. The attorney did not return a call for comment, and Roberts could not be reached.

"All employment decisions involving plaintiffs were constitutional, lawful, not the result of any improper purpose or motive, and not in retaliation for political expression," the sheriff's attorney wrote in the filings.

Roberts said that some of the fired deputies had unsatisfactory work performance and that the campaigning had disrupted the workplace.

U.S. District Judge Raymond A. Jackson issued a summary judgement against Carter and the other plaintiffs in January. In his explanation of the ruling on Carter's claims, he dismissed the argument that a Facebook like is constitutionally protected speech.

"Merely 'liking' a Facebook page is insufficient speech to merit constitutional protection," Jackson wrote. "In cases where courts have found that constitutional protections extended to Facebook posts, actual statements existed within the record."

Facebook took issue with the decision, saying in its filings that likes are the "21st-century equivalent of a front-yard campaign sign." (Washington Post Co. chairman and chief executive Donald E. Graham is a member of Facebook's board of directors.)

Jackson's decision has also drawn criticism from some legal experts. Eugene Volokh, a law professor at the University of California at Los Angeles, said firing government employees for speaking out about matters of public concern is generally unconstitutional.

He said there are some exceptions, such as when a high-ranking employee's political affiliations are relevant to the job, or if the speech greatly disrupts the workplace or diminishes public confidence in the government agency.

In the Sheriff's Office case, Volokh said, Jackson upset a precedent with deep roots in U.S. law.

"The judge's rationale that a like on Facebook is insufficient speech is not right," Volokh said. "The First Amendment protects very brief statements as much as very long ones. It even protects symbolic speech, like burning a flag."

Volokh, like the ACLU, says liking is similar to putting a bumper sticker on a car, so it should be protected. He said he thinks the 4th Circuit will probably overturn the district judge's ruling — but if it does not, it would be a significant moment.

"If the 4th Circuit agrees with the judge — that liking is not protected speech — that would suggest an overturning of precedents," Volokh said. "It would be interesting to see what the Supreme Court would do with that decision."

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Jennifer Jenkins contributed to this report.