11 April 1961
On 11 April 1961, Nigeria imposed a trade boycott on South Africa, due to objections against South Africa's apartheid policy. In early 1960, Nigeria had decided to ban all imports from South Africa, and was reportedly in the process of refusing facilities for South African aircraft. However, this process became unnecessary as South Africa decided to bypass Nigerian airports. Trade sanctions and boycotts aimed to put pressure on the South African government to abandon its discriminatory racial policies. These policies were harshly criticized in the international community - especially after the Sharpeville Massacre in 1960.
References

(1965), "Notes on the Origins of the Movement for Sanctions against South Africa", from geocities.com, [offline], Index unavailable [Accessed: 01 April 2009]|Nigerialogy, (2013), This Week in Nigerian History, from Nigerialogy, 20 April [online], Available at www.nigerialogy.com [Accessed: 10 April 2014]