Uuncertainty about the structure of the proposed Indigenous Voice to parliament will likely act as a barrier to companies campaigning in favour of the referendum, leading directors say.

In sharp contrast to the same-sex marriage debate in 2017, which attracted the public support of more than 1000 organisations, including the major banks, big professional services firms and companies such as property company Mirvac and General Electric, employers have taken much more of a back seat on the Voice referendum, at least publicly.