Addressing a press conference, Mulayam said, "It would be anti-democratic to pass the bill in its present form. It is a ploy to block entry of Muslims, backwards, Dalits and poor in Parliament and State Assemblies."
"The Congress, by taking the Bharatiya Janata Party's support for the Bill, had proved it was not secular," he alleged.
"The Samajwadi Party was never against the Bill in principle, but in its current form it is against minorities," he said.
Rashtriya Janata Dal (RJD) leader Lalu Prasad has also said his party will oppose the Bill in Parliament.
"No country in the world has reservation for women. I don't know what example is our country trying to set. When the Bill comes to be vote we will oppose it in our capacity," he said.
The UPA government will table the legistation in the Parliament on Monday, Mar 8 coinciding with International Women's Day.
The bill seeks to provide 33 per cent reservation to women in Parliament and state assemblies on a rotation basis.