Opposition leaders, including those from the Congress, NCP, Trinamool Congress (TMC), Samajwadi Party (SP), RJD, National Conference and the Left parties, met on the eve of the winter session of Parliament to discuss key issues to be raised in Parliament.
It was "indeed shocking" that the Election Commission had failed to uphold its constitutional mandate, the leaders said in a statement.
Instead of taking action for violations, the poll panel had allowed violations by the ruling party.
"This attitude of the EC has cast ominous shadow on the credibility of the EC and the integrity of the electoral process," the leaders said.
More From This Section
The opposition leaders also expressed their disappointment and "outrage" over the disqualification of Sharad Yadav and Anwar Ali from the Rajya Sabha.
It was a hasty move taken without following due process, they said, describing the decision as "unfair and unjust".
The meeting was held in the chamber of the Leader of Opposition in Rajya Sabha, Ghulam Nabi Azad.