The lawmakers protested near the main gate of Parliament.
Raising slogans against Trinamool Congress, they alleged that political killings of Left activists were taking place in the state after the party came to power.
Senior leaders Sitaram Yechury and Basudev Acharya were among those who participated in the protest.
Yechury told reporters that "false" cases were registered against Left activists and ex-MLAs in the state.
"A systematic political harassment is going on in the state against the democratic system. We want this to stop immediately," he said.
New Delhi: Left MPs on Thursday staged a dharna in Parliament premises to protest against the "harassment" meted out to their activists allegedly by the Trinamool Congress government in West Bengal.
First Published: Thursday, March 22, 2012, 12:36