The government opted for the ordinance route on Tuesday after a bill on the same issue could not be passed in the monsoon session of parliament.
Terming the step "uncalled for", senior BJP leader Yashwant Sinha said: "The government stands condemned in the eyes of the people of the country for taking this unconstitutional and immoral route."
He said: "If the government had any reservations on that order, it should go back to the Supreme Court and ask it to review it."
"In this case, I would say that (review) also may not be necessary because we are all faced with declining standards in politics and criminalisation of politics, and it should be the combined duty of all of us to ensure that this is stopped," Sinha told a news channel.
Leader of Opposition in the Lok Sabha Sushma Swaraj tweeted: "Union cabinet has approved an ordinance on convicted MPs. We are opposed to this. We request the president not to sign this ordinance."
CPI-M leader Sitaram Yechury said that at an all-party meeting convened to discuss the issue, it was decided that if somebody has been convicted in a lower court, it is possible that he gets reprieve from the higher court.
"But, we had said there should be a discussion and the matter should be brought before parliament," he said.
Aam Aadmi Party (AAP) leader Manish Sisodia said: "We will not give any ticket to any corrupt leaders. It is our challenge that in all the 70 Vidhan Sabha seats (in Delhi), we will have clean politicians and even if any one (corrupt person) comes, we will cancel his nomination."
Information and Broadcasting Minister Manish Tewari took to Twitter and responded: "The constitutionality or otherwise of legal enactments are tested in constitutional courts and not in the BJP's moat."
Tewari added: "Unsolicited advise is neither appreciated nor taken seriously. These are the first principles of the legal profession, advise of leader of opposition amusing/surprising."
The ordinance would save the elected members from disqualification from house, but would take away their perks. The ordinance, once approved by President Pranab Mukherjee, will have to be passed by parliament during the winter session, likely November-December.