NEW YORK -- His first impulse was to dismiss the ominous email as a prank, says a young Iranian-American named Koosha. It warned the 29-year-old engineering student that his relatives in Tehran would be harmed if he didn't stop criticizing Iran on Facebook.

Two days later, his mom called. Security agents had arrested his father in his home in Tehran and threatened him by saying his son could no longer safely return to Iran.

"When...