Associated Press employees have been warned to not share their opinions via social media, Poynter reports, lest they damage the reputation of the 165-year-old international news network.

Jim Romenesko, writing for Poynter.org, relayed a memo from Tom Kent, the deputy managing editor for standards and production, that focused on social network posts by AP "staffers" on the Casey Anthony trial and the successful gay marriage vote in the New York Senate. "These posts undermine the credibility of our colleagues who have been working so hard to assure balanced and unbiased coverage of these issues," wrote Kent. He added that the organization's rules "state that anyone who works for AP must be mindful that opinions they express may damage the AP’s reputation as an unbiased source of news."

The Editors Web Log reports that two international media giants have had to face the impact of social media. The BBC was considering banning its creative talent from using social media, while Reuters has appointed an editor to improve its social media presence. In May, Bloomberg, Freedom Communications, Inc. and the Toronto Star all issued social media guidelines to their staffs. The American Society of News Editors also recently launched guidelines for social media use.

While social media outlets like Facebook, Twitter and now Google+ have become increasingly popular tools for journalists, reporters and commentators have been known to get themselves into trouble when they share caustic opinions. Veteran CNN correspondent Octavia Nasr was fired a year ago after she Tweeted a comment that was considered to be inappropriate.

In April this year, in what may be the first case of its kind, the National Labor Relations Board said it would file a complaint against Reuters after it had reprimanded a reporter for sending a Tweet that criticized the company.

See this Knight Center Twitter feed for more cases about freedom of expression and social media.