The main reason why the Wagner Act was passed into US federal law as part of FDR's New Deal was because FDR believed the Great Depression had been caused by low

The main reason why the Wagner Act was passed into US federal law as part of FDR's New Deal was because FDR believed the Great Depression had been caused by low wages. Specifically, lack of purchasing power on the part of working people due to low wages was and is widely considered a major cause of the Depression. Allowing unions rather than suppressing them by state force or allowing corporations to suppress them by private force was seen as a way to stabilize the economy and increase the profitability of corporations by driving up wages which would actually help business because consumers would actually be able to afford their products.