Anas Sarwar has admitted he "regrets" voting in favour of gender recognition reform and would have opposed it "knowing what we know now".
The Scottish Labour leader made the comments as he expressed his support for nurse Sandie Peggie amid an employment tribunal with NHS Fife after she objected to a transgender doctor using the women's changing room.
Sarwar, The Times reports, said: “No nurse should ever face disciplinary action for refusing to share a changing room.”
It comes as it emerged Peggie is facing a disciplinary hearing over the matter.
Sarwar went on: “If we are going to stop falling into divisive culture-war politics, and we are going to make progress as a nation, we have got to say, quite clearly, we support single-sex spaces based on biological sex, we respect the Equality Act."
Speaking on the Holyrood Sources podcast, Sarwar told the Holyrood Sources podcast that Labour had mistakenly accepted assurances from Scottish ministers that the Gender Recognition Reform (Scotland) Bill complied with the Equality Act, which was incorrect.
He said his party should have opposed the bill after the Labour amendments were rejected.