13 June 1950
The National Assembly voted in favour of the separation of  the people of South Africa into four distinct races (White, Black, Coloured, and Indian) through the Population Registration Act No. 30 of 1950. It further voted to divide South Africa into separate areas (for the exclusive use of each race) through the Group Areas Act No. 41 of 1950. Both these Acts commenced on 7 July, 1950. On 20 February, 1950 the Population Registration Act was read for the first time in Parliament. Subsequently, it became the cornerstone of the Apartheid policy. An office was set up to oversee the classification process.
References

South African History Online, ‘The Population Registration Bill is read for the first time’, [online], available at www.sahistory.org.za (Accessed: 17 May 2013)|

Boddy-Evans, A. ‘This Day in African History: 13 May’, from About African History, [online], available at https://africanhistory.about.com (Accessed: 17 May 2013)