Sen. Mark Kelly (D-AZ), a top contender to be Vice President Kamala Harris’s running mate, said Wednesday he’s all in for pro-labor legislation known as the PRO Act and insisted he always has been.

But Kelly is one of three Senate holdouts in the Democratic Caucus yet to co-sponsor the measure that proponents say would make it easier for workers to form and join unions, and in years past has expressed opposition to passing the bill in its current form.