The Union signed defender/midfielder Sheanon Williams to complete their 24-man roster.
The 20-year-old joined the Union from the Harrisburg City Islanders, the team's USL-2 affiliate. Contract details were not disclosed.
Williams represented the United States in two youth World Cups, the Under-17 World Cup in Korea (2007), where he played for former head coach and current Union coach John Hackworth, and the Under-20 World Cup in Egypt (2009).
The Union host Chivas de Guadalajara in a friendly at 8 p.m. Wednesday. Chivas, currently a finalist in the Copa Libertadores championship, is Mexico's most successful team, having won a record 11 titles since the start of the professional era.