SAG-AFTRA, which represents more than 165,000 actors, journalists and other media professionals, issued a statement on Tuesday calling on law enforcement officials in Ferguson, Mo., to "permit journalists the freedom to do their jobs."
"Just cuffed and searched as we said we were leaving as he asked," Financial Times reporter Neil Munshi tweeted on Sunday, attaching a link to a Vine video of the incident.
Robert Klemko, of Sports Illustrated, posted a photo on Twitter of the plastic "handcuffs" used by police to detain him.
On Monday, Getty Images photographer Scott Olson was also arrested for reportedly not being in the media area.
Last week, after Washington Post's Wesley Lowery and Huffington Post's Ryan J. Reilly were taken into custody by Missouri police, President Obama addressed journalists' rights in a speech.
"Here in the United States of America, police should not be bullying or arresting journalists who are just trying to do their jobs," he said in a news conference.
SAG-AFTRA echoed similar comments.
"Journalists have an obligation to report what is happening in their community, and the world," the union said in its statement.