Nearly 67 percent of voters in the northeastern Swiss canton voted in favour of the new law, according to official results, paving the way for it to follow the example of the southern canton of Ticino, where a law was introduced two years ago that appeared to be aimed at burqas and other Muslim veils.
A text stipulating that "any person who renders themselves unrecognisable by covering their face in a public space, and thus endangers public security or social and religious peace will be fined" was adopted by lawmakers in St. Gallen late last year.
That law passed the regional parliament with support from the populist right and centre parties -- but the issue was put to the people after the Green Party and Young Socialists demanded a referendum.
Switzerland's government last year opposed an initiative aimed at creating a nationwide burqa ban, saying it should be up to the regions to determine if such measures are appropriate.
Voters across Switzerland are however expected to be called to vote on the issue next year after the populist rightwing Swiss People's Party gathered the 100,000 signatures needed to put any subject to a referendum as part of Switzerland's famous direct democratic system.