"I welcome the TDP's decision to leave the NDA. The current situation warrants such action to save the country from disaster," the Trinamool Congress president tweeted.
In protest against the union government's refusal to grant Special Category Satus (SCS) to Andhra Pradesh, the TDP on Friday morning announced its decision to break away from the Narendra Modi government.
The party's politburo unanimously took the decision during a teleconference with party president N Chandrababu Naidu.
Mamata then called upon all opposition parties to unite against atrocities, economic calamities and political instability.
"I appeal to all political parties in the Opposition to work closely together against atrocities, economic calamity and political instability," she said.
The TDP is also likely to move a no-confidence motion against the Modi government over the injustice meted out to the state on Monday.
Meanwhile, the BJP has called all its MPs in Andhra Pradesh for an emergency meeting in the capital.