Faxes blaming South Korea for the Nov. 23 artillery attack on Yeonpyeong Island started arriving this month at the companies, South Korean Unification Ministry deputy spokeswoman Lee Jong-joo said Wednesday.
"Responsibility for the attack lies with the South," the faxes said. "Groups in the South should rise up against the South Korean government."
The ministry says 15 organizations -- including two religious groups, seven trade companies, five civic groups and one media organization -- had received the faxes, CNN reported.
The ministry said 50 to 80 companies probably received the messages but not all have reported them to the government yet.
Most of the companies receiving faxes had prior contact with North Korea through inter-Korean events or business operations, Lee said.