"It is a cruel blow on people who are already suffering from severe price rise. The Left parties have called upon all party units to immediately organise powerful protest actions," CPI-M General Secretary Prakash Karat told PTI.
His senior colleague Sitaram Yechury said the move was a "criminal additional burden" on people's livelihood.
Leaders of the CPI-M, CPI, RSP and Forward Bloc, who met here, also opposed the move, with CPI leader D Raja saying this was a "prelude to hike the prices of diesel and other petroleum products".
Observing that the hike had been effected "even before a day had passed after the Budget Session of Parliament ended", he said the government's move was "completely unethical and undemocratic. It shows how totally insensitive the Congress- led UPA government has become to the sufferings of the common people."
Blaming the government for the fall in the value of the rupee, Raja said "all the economic advisors to the Prime Minister and Finance Minister will have to be blamed for the massive mismanagement of the country's financial and monetary policies."
State-owned oil firms said they will raise petrol price by Rs 6.28 per litre excluding local sales tax or VAT. The hike translates into Rs 7.50 per litre in Delhi.