Earlier this week, hundreds of Maoists staged a sit-in protest in front of a government building in the capital.
The Maoists want the current government to resign.
The former rebels, who fought a decade-long civil war with the state before winning elections, stepped down in May 2008 after Ram Baran Yadav, the Nepalese president, overruled their attempt to sack the army chief.
Since then, the Maoists have sought a reversal of the ruling and a public apology from Yadav, a member of the rival Nepali Congress party whom they accuse of acting unconstitutionally.
The Maoists also accuse the government of opposing the integration of thousands of activists into the national army, a key component of the peace deal under which the Maoists laid down their arms three years ago.