In 1917, it absorbed several small unions and thereafter opened admission to all workers in the industry.
In 1924, it was joined by the United Shoe Workers of America union.
Over the following years, it gradually absorbed the Amalgamated Shoe Workers of America union, one city at a time.
However, a substantial minority of the union disagreed with the merger and continued as the SWPU.
In 1937, this merged with the USLWU, to form the United Shoe Workers of America.