Women's Enfranchisement Act, 1930
The Women's Enfranchisement Act, 1930, was an act of the Parliament of South Africa which granted white women aged 21 and older the right to vote and to run for office. It hence diluted the voting power of non-white people in the Cape Province by effectively doubling the number of white voters.
Source: Wikipedia — Women's Enfranchisement Act, 1930 (CC BY-SA 4.0)