51 of 1968, which was also known as the Prohibition of Improper Interference Act, and was later renamed the Prohibition of Foreign Financing of Political Parties Act), was a piece of apartheid legislation in South Africa that sought to prevent racial groups from collaborating with each other for a political purpose.

This act is thought to have been enacted by the ruling apartheid government to prevent the strong growth of the Liberal Party of South Africa (LPSA), which was made up of South Africans of various races who were against the racially divisive policies of the Apartheid regime government.

Initially referred to as the South African Liberation Association, the party sought to repeal racially discriminating legislation and ensure access to health care, quality education, voting rights, and equal human rights for South Africans of all races.

The act also prohibited parties from receiving funding or donations from foreign organizations or people.

The repealing of the Act was as a direct result of increased political and financial pressure on the National Party of South Africa to end its racially divisive policies.