"We can't knowingly and deliberately commit an unconstitutional act, make a bill which is against the Constitution," Sinha said.
He however added that the BJP was in favour of a strong Lokpal.
The veteran leader accused the government of trying to derail the process of passage of the bill by moving a last minute addition on minority reservation.
"The manner in which the bill has been brought, the amendments moved by corrigenda, are all to my mind, efforts on the part of government to derail the process of passage of the bill," Sinha told a news channel.
The BJP leader also pointed out that independence of the Central Bureau of Investigation (CBI) from government clutches was important and said the inclusion of state Lokayuktas in the act was unconstitutional.
The BJP is to move several amendments to the bill, which will include amendment against minority quota, against inclusion of Lokayukta under Lokpal, and for inclusion of the CBI under the anti-graft body.
Asked about Anna Hazare's three-day hunger strike in Mumbai, Sinha said the bill should be debated on its merits irrespective of the agitation.
"Parliament should consider it most objectively, irrespective of the fact that Hazare is protesting outside, they must debate it on merits, or defects and get the bill passed," he said.
Leader of the Opposition in the Lok Sabha Sushma Swaraj from the BJP will initiate the debate on the Lokpal bill in the Lower House.
New Delhi: Senior Bharatiya Janata Party (BJP) leader Yashwant Sinha termed the Lokpal Bill as "unconstitutional" ahead of Tuesday's debate in Parliament over the contentious legislation.
First Published: Tuesday, December 27, 2011, 11:42