The CPI-M said on Thursday that the nationwide strike by road transport workers was "successful and massive" and involved some 20 million employees.
"Workers belonging to the public transport, private buses, auto-rickshaws, taxis and trucks numbering two crore workers participated in the strike," the Communist Party of India-Marxist said in a statement.
"The workers were protesting against the Road Transport Safety Bill 2015, the passage of which would enable the privatization of the transport sector, to the detriment of the state-owned transport corporations and other bus operators," it said.
"Some of the provisions provide harsh penalties to the drivers and can be liable to misuse," it added.
The CPI-M urged the government to discuss the provisions of the bill with representatives of the transport sector "instead of trying to push through the bill in parliament".