Job reservation is one means by which the South African government (under the apartheid system of maintaining white supremacy at the cost of the black majority) limited job opportunities for blacks by prohibiting the replacement of workers of one race by workers of another race; by compelling employers to maintain a fixed percentage of workers of a particular race; by reserving any class of work of specific jobs or work generally for members of a specific race; and by fixing maximum, minimum, or average numbers or percentages of persons of a specified race who may be employed in any factory or industry or other places of employment. These restrictions were applied under Section 77 of the Industrial Conciliation Act of 1956; all but five of them were abolished in 1977, but this had little effect as the general industrial colour bar based on long-standing attitudes and attitudes was underpinned by formal closed shop agreements between white trade unions and major companies. These affect the majority of black workers far more seriously.