"The constitution allows only one recourse to remedy the situation. Since there is no other way to protect the institution except to move on impeachment motion, we, members of the Rajya Sabha, do so with a heavy heart," said the Congress. Seven of the Rajya Sabha members have resigned since the signatures were collected.

Former Prime Minister Manmohan Singh's signature is not on the impeachment motion. "We didn't involve Manmohan Singh intentionally as he is an ex-PM," said Congress leader Kapil Sibal.

The Congress emphatically denied the move was linked in any way to the decision of a Supreme Court bench led by the Chief Justice on Thursday that the death of judge BH Loya will not be investigated. Judge Loya was deciding on murder charges against BJP president Amit Shah when he died of a heart attack in 2014.

The opposition petition lists five "charges" including the assigning of sensitive cases to handpicked judges.

These allegations were raised in January by four top judges who publicly criticised the Chief Justice and accused him of abusing his position as "master of the roster". The trigger for their press conference was the judge Loya case, which was later reassigned.

On Thursday, the Congress had expressed disappointment with the judge Loya case verdict, calling it a "sad letter day in India's history". Party chief Rahul Gandhi tweeted that the "truth had a way of catching up" and it would, with Amit Shah.

The parties that have signed the motion are Congress, Mayawati's BSP, Samajwadi Party, Sharad Pawar's NCP, CPI, Indian Union Muslim League (IUML) and Jharkhand Mukti Morcha (JMM). Sources say the opposition is divided on this; parties like the Trinamool Congress, DMK, and Lalu Yadav's RJD are against impeachment.

Former Attorney General Soli Sorabjee said impeachment can only be on grounds of misbehaviour. "One cannot bring an impeachment motion against a judge because you think he has given a wrong judgment," he said.

The Constitution details the process of impeachment for the Chief Justice of India on the ground of proven misbehaviour or incapacity.