However, the flag missed the vehicle as it sped fast, police said.
According to police, a group of CPI(M) activists, who were waiting to wave black flags at Finance minister K M Mani, who was also attending the function in connection with the inauguration of a swimming pool, hurled a flag as the CM's vehicle passed at nearby Vedivechan kovil.
Police said the activists had mistaken Chandy's vehicle for Mani's car.
CPI(M) has been protesting since the past few months against Mani, who is facing allegations of bribery with regard to renewal of bar licenses.