The bill was passed by State Duma lawmakers in a 346-99 vote Friday, against a required minimum of 226, but still needs the approval of the upper house, the Federation Council, to become law.
Central Electoral Commission Chairman Alexander Veshnyakov challenged parts of the bill, while Federation Council Speaker Sergei Mironov called it dubious.
The new legislation, which would abolish the 20% voter turnout, and ban negative campaigning on television and voting by absentee ballots, is sponsored by the pro-Kremlin United Russia party and the ultranationalist Liberal Democratic Party.
Veshnyakov said it would be premature to abolish the bottom limit for voter turnout, but spoke in favor of other changes proposed in the bill.
"The prospective changes include some positive, indisputable proposals, but there are objectionable proposals as well, ones that could be called premature. The decision to remove the voter turnout threshold is among those I consider to be premature," he said.
Veshnyakov said that in the future, the turnout minimum could be reduced to 5%, but not lower.
The Federation Council speaker objected to the idea of scrapping the turnout threshold, and was equally critical of the idea to ban negative campaigning.
Mironov described as "dubious" arguments made by the bill's backers, who "believe it is unacceptable that a party with no realistic chance of making it into the State Duma gets registered, and runs a campaign only to sling mud at everyone."
The top election official said, however, that the bill would not compromise Russia's ability to hold free and fair elections.
"Even with these changes in effect, the new bill will allow the holding of democratic polls," he said.
But leaders of the Duma's Communist Party faction launched harsher criticism against the proposals.
"This will be the final blow from the incumbent government, one that will render the term 'election system' utterly meaningless," said Ivan Melnikov, the deputy chairman of the party's central committee.
With the threshold scrapped, "the State Duma would reflect the position of 'ballot-casting individuals,' not the will of society," he said.
