There are "significant concerns" about how politicians will be elected in Wales, after a council warned it could be "undemocratic".
A report by the Senedd's cross-party reform bill committee concluded that plans should proceed to the next stage, but it said amendments should be considered to ensure "greater voter choice and improved accountability".
As part of the evidence the committee considered, Flintshire County Council said the new system could be "undemocratic and could deter people from standing and voting in an election".
The plans are part of a drive by the Welsh government to reform the country's democracy - including increasing the number of members from 60 to 96.
This has been criticised by some opposition members as a waste of money, but the government argues more members will mean more scrutiny of its policies.
Welsh government estimations put the cost of implementing the legislation between £99,683,800 and £119,631,700 over an eight-year period.
Under the proposals, members would be elected from closed lists, with some politicians warning parties will have more influence over those elected.
The number of Welsh constituencies is set to drop from 40 to 32 at the next Westminster election.
For elections to the Senedd, these 32 will be paired to form 16 constituencies.
Six members will be elected for each of those from closed lists, using the D'Hondt formula.
That method divides the number of votes cast for each party by the number of seats the party has already won, plus one.
David Rees, chair of the Senedd's reform bill committee, said the group was united in its concerns about the impact on "the level of voters' ability to choose who represents them".
"Getting the electoral system right is fundamental to the health of democracy in Wales, and we have significant reservations about whether closed list elections represent a positive step forward," he added.
Andrew RT Davies, leader of the Welsh Conservatives, said expanding the Senedd was a "huge distraction".
"They should be focusing on the priorities of people in Wales, such as the dire performance of our Welsh NHS, schools and economy, not more politicians," he added.
Sky News has asked the Welsh government for its response.