ZURICH—A Swiss parliamentary body Wednesday further complicated Switzerland's handling of a US settlement to hand over account details on 4,450 wealthy US clients of UBS AG by recommending Swiss voters be allowed to vote on it if they want to.

Switzerland's business and economics committee voted 12 to seven in favour of recommending lawmakers pass UBS's August settlement with the US, but were deadlocked over allowing a referendum, which would delay the settlement by at least 100 days. The commission's president, Hansruedi Wandfluh of the conservative People's Party, cast the deciding vote supporting a referendum, deputy committee secretary Alexandre Fuezessery said.