Why was there constitutional crisis during 1955 to1956

The Coloured vote constitutional crisis, also known as the Coloured vote case, was a constitutional crisis that occurred in the Union of South Africa during the 1950s as the result of an attempt by the Nationalist government to remove Coloured voters in the Union's Cape Province from the common voters' rolls. It developed into a dispute between the judiciary (in particular the Appellate Division of the Supreme Court) and the other branches of government (Parliament and the executive) over the power of Parliament to amend an entrenched clause in the South Africa Act (the constitution) and the power of the Appellate Division to overturn the amendment as unconstitutional. The crisis ended when the government enlarged the Senate and altered its method of election, allowing the amendment to be successfully enacted