"The Government has violated the tripartite agreement as they have not withdrawn the political cases against Morcha leaders from 2007-2011," GJM President Bimal Gurung said in a Facebook post.
"Our 3 GJM MLAs will not attend State Assembly to condemn the unwanted arrests of 721 innocent Gorkhaland supporters in old cases," Gurung said.
A three-day extended budget session of the Assembly would begin on August 26.
Speaker Biman Banerjee rejected during the day a plea by the three GJM MLAs, who at present sit on the treasury bench with the ruling Trinamool Congress, to switch over to the opposition.
Banerjee told reporters in Kolkata here that the prayer was rejected on technical grounds since the assembly rules were not followed.
He said that the letter was written to him by Gorkha Janmukti Morcha General Secretary Roshan Giri and not by the MLAs themselves or by the legislature party.
Meanwhile, three GJM leaders, including a leader of its youth wing, were arrested here in old cases pending against them.
Santosh Tamang, a leader of Gorkha Yuva Morcha, was arrested from his home at Garidhura in Kurseong sub-division of the hills, police said.
They were arrested in cases of arson, damage to government property and for threatening people in 2011.
The total number of arrests have crossed 700, according to police.
