The Devendra Fadnavis government won the trust motion in Maharashtra Assembly on November 12 through a voice vote.
Opposition Shiv Sena and Congress had reacted angrily to the way the vote was won and accused BJP of failing to prove its majority in the House and "strangulating democracy".
Both parties had pressed for division of votes.
Sawant said "division of votes (ballot voting) is a must for a minority Government to prove its majority. The constitutionally ordained process was to hold test on the floor of the House. Besides, the test should be openly and objectively demonstrated and ascertained publicly in House."
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Citing precedents, he said as per the Sarkaria Commission, confidence in a ministry is to be determined in the House. If a Chief Minister fails to do this, the Governor is duty-bound to form an alternative ministry.
In the present case, Sawant said, the ruling BJP should have gone for division of votes during the floor test to demonstrate majority. "This government is unconstitutional and illegal, And has no right to stay in office."
Sawant asked Congress to handle the issue rising above party politics. "Democratic principles and rules are at stake and the Constitution must be upheld. Parties and Governments come and go. But anti-democratic and unconstitutional precedents should not be set as they are dangerous."
The ex-Judge maintained that even the voice vote was not carried out as per norms.