(CNN) -- The mothers of two Americans accused of espionage in Iran say they started a hunger strike Thursday amid fears that their sons are in grave danger.
Shane Bauer and Josh Fattal have been imprisoned in Iran for more than 21 months.
A trial for the 28-year-old men was supposed to happen last week, but it was delayed without an explanation after they were not brought to the courthouse.
"We have not had any news about Shane and Josh for many months, and we are terrified that they have now gone on (a) hunger strike to protest against this latest, devastating delay," said Cindy Hickey, Bauer's mother.
"We're worried that they are not getting proper medical care and that their lives may be in danger."
Fattal's mother, Laura Fattal, urged Iran to free the two.
"Whoever is to blame for preventing our sons' release is bringing shame on Iran," she said. "Shane and Josh have been denied justice and compassion for far too long. Today we begin a hunger strike and stand with our sons to urge Iran to stop punishing them --and our families -- for no reason."
The two were charged with espionage after being arrested in July of 2009 while hiking along an unmarked border between Iran and Iraqi Kurdistan. A third hiker, Bauer's fiancee Sarah Shourd, was also arrested. She was released last year.
Shourd will take over the hunger strike Saturday, the family said.