In the early 1940s, legal pressure forced the studios to replace seasonal block booking with packages generally limited to five pictures. Restrictions were also placed on the majors' ability to enforce blind bidding. These were crucial factors in the progressive shift by most of the Big Five over to A-film production, making the smaller studios even more important as B movie suppliers. Genre pictures made at very low cost remained the backbone of Poverty Row, with even Republic's and Monogram's budgets rarely climbing over $200,000. Many smaller Poverty Row firms folded as the eight majors, with their proprietary distribution exchanges, now commanded about 95% of U.S. and Canadian box office receipts.