Kenneth Bae's family says the 44-year-old's health is failing and he needs to be released before it's too late.
Bae, described by friends as a devout Christian and a tour operator, was arrested in early November in Rason, a special economic zone in North Korea's far northeastern region bordering China and Russia, North Korea said.
Bae's sister, Terri Chung, has spent the last nine months trying to find a way to free her brother. She's had just two phone calls and five letters since he was imprisoned.
Chung said her brother, a tour guide, was doing nothing wrong when he was arrested.
"He's done that trip probably at least 15 times," she said. "That was his livelihood and his profession."
Chung believes the government imprisoned Bae because he was sharing his religious beliefs, which is considered a crime against the government.
"He's working in the fields, farming work for 8 hours a day, 6 days a week," she said.
Bae suffers from severe back pain, diabetes, an enlarged heart and liver problems, according to Chung.
The last time anyone saw Bae was in a July prison interview recorded by a pro-North Korean group.
"Just devastated thinking about that," Chung said. "He just looks so broken."
Chung is counting the days until her brother can return home, and she prays it happens soon.
"How much longer can his body just withstand the physical labor and the strain from it?" she said.
Chung and the rest of Bae's family will hold a vigil on Saturday night at 7 p.m. at Quest Church in Seattle. The entire community is invited to attend.