While the American teachers’ unions are commonly understood to be guarantors of public school teachers’ job security through their backing of teacher tenure laws, the relationship between tenure and teachers’ organizations is historically contingent. This article shows how in 1937 Pennsylvania teachers pushed their state legislature to pass what was at the time the most empowering teacher tenure law in existence. Using primary documents, the article examines how nonunionized teachers politicized tenure in the early 1930s, before the New Deal reshaped the political environment. Women activists from Philadelphia’s AFT Local 192 successfully lobbied the legislature in Harrisburg in 1937 to pass a far-reaching tenure law that not only guaranteed due-process rights for teachers, but did so without allowing for a probationary period and without exception for married women teachers. Pennsylvania’s teacher unionists fought against efforts to reform the law in the years that followed.