In 1951, it was illegal for non-profit tax-exempt organizations to engage in lobbying activities. "We couldn't do any substantial amount of lobbying and keep our tax-exempt status," explained AWI founder Christine Stevens, who is referred to as the "Mother of the Animal Protection Movement." Her solution was to form an organization that did not require a tax-exempt status, one that would inform senators, representatives and the public about animal issues. The Society for Animal Protective Legislation (SAPL) became the first organization founded in the United States specifically to lobby on behalf of animals. If legislators wanted to know more about issues pertaining to humane slaughter, leghold traps or endangered species, they contacted SAPL. Because of changes in tax laws, in 2003, SAPL merged with the Animal Welfare Institute, bringing together two of the oldest and leading animal protection organizations in the United States.