State Sen. Billie Sutton said in a Friday statement to The Associated Press that such laws are a "solution in search of a problem."
Lawmakers have previously proposed limiting which school facilities transgender students could use, a likely issue in the 2018 governor's race.
Sutton's view of a so-called bathroom bill diverges from the two top Republicans in the GOP gubernatorial primary. Attorney General Marty Jackley and Congresswoman Kristi Noem this week offered support for the idea.
A key conservative group plans to wait until the 2019 session to pursue such restrictions when a new, potentially more favorable governor will be in office.
Retiring Republican Gov. Dennis Daugaard has opposed such bills.
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A Democratic governor candidate is speaking out against restricting which facilities transgender students could use in South Dakota schools.