In a statement here, LDF convenor Vaikom Viswan said the Centre's decision amounted to "a declaration of war" on the people.
"It cannot be accepted at all. LDF will organise protests throughout the state against the decision and will observe a hartal on September 15," he said.
Meanwhile CPI(M) state secretary Pinarayi Vijayan said the decision to hike diesel price was meant to bring undue profit to private oil companies.
CPI state secretary Pannyan Ravindran also called upon the party workers and people to come out in protest against the hike.
Meanwhile, DYFI workers took out protest marches in some parts of the state against the hike in diesel price.
