A CPI(M) leaders son and his journalist daughter-in law were attacked allegedly by protesters trying to enforce a shutdown Saturday, the police said.
Julius Nikithas and wife Saniyo Manomi, working with a leading Malayalam news channel, were attacked at Kuttiady as they were going to a hospital in a car to visit a patient, they said.
Mr Nikithas, son of party district secretary P Mohanan, suffered head injuries, police said, adding that Ms Manomi was also injured.
The couple have been admitted to the government medical college hospital.
The CPI(M) alleged that they were attacked by activists belonging to the Sangh Parivar.
A case has been registered against ten people allegedly involved in the attack, police said.
Right-wing Hindu outfits observed a dawn-to-dusk hartal in Kerala Saturday in protest against the "preventive detention" of Hindu Aikya Vedi state president P Sasikala who was on a pilgrimage to the Sabarimala Lord Ayyappa temple.
State-owned and private buses and auto-rickshaws were off the roads in most parts of the state due to the hartal.
At various places, hartal supporters forcibly downed shutters of shops, prevented vehicles from plying, causing hardship to long distance travellers reaching railway and bus stations.
The Bharatiya Janata Party had extended support to the shutdown.