The ultras opened fire on the 'Yatra' when it reached near forested Geedam Ghati area on way to Jagdalpur, injuring local worker Gopi Vadhwani, they said.
Senior leaders, including state unit Congress chief Nand Kumar Patel, former Union minister Vidyacharan Shukla and others, were part of the Yatra when it was attacked, according to a senior police official.
Chhattisgarh Congress media cell president Shailesh Trivedi said it was matter of investigation whether Naxals were involved in the attack.
"Naxals have opposed both BJP's Vikas Yatra and Congress' Parivartan Yatra. However, the state government provided security only to BJP's Yatra and not to the one organised by Congress. Had it been provided security, today's incident would not have happened," he said.
Trivedi said he was trying to contact the party leaders who were part of the Yatra but was unable to do so as the incident occurred in forested area.
Congress had launched Parivartan Yatra on April 12 in the state where Assembly elections are due by year end.