Joining them is Sarah Shourd, one of three Americans detained by Iranian authorities when they allegedly strayed into Iranian territory during a hike in July 2009, the Los Angeles Times reported Saturday.
Shroud spent 14 months in an Iranian prison cell before being released on $500,000 bond. Her fiance, Shane Bauer, and their friend Joshua Fattal, remain in custody in Tehran.
The mothers of Bauer and Fattal, Cindy Hickey and Laura Fattal, announced May 19 they were embarking on a "rolling hunger strike" and by Friday more than 270 people signed up to join them through Facebook.
"They have committed no crime," Shourd said. "They have done nothing wrong, and they don't deserve to be there a minute longer than I was. We hope that news of the hunger strike will get to Shane and Josh and make them feel less alone."