According to a tweet by RSL beat reporter, and Salt Lake Tribune blogger, Michael C. Lewis, the Philadelphia Union have a schedule change, as the team's April 23 match in Salt Lake is now on September 3.
Citing "preparation" for Real Salt Lake's upcoming CONCACAF Champions League game against Mexican side Monterrey, Lewis says MLS moved the game from April to September. Salt Lake has their second leg against Monterrey in the finals of the CCL on April 27.
Jonathan Tannenwald, of Philly.com and its soccer blog The Goalkeeper, pointed out over Twitter (through The Goalkeeper's account) that now the game is scheduled for a off-week for MLS. September 3 is a FIFA international break for teams in MLS. The league appears to have caused a problem for the two teams later in the season.
If the game between the Union and Salt Lake had not been rescheduled, the 2009 MLS champions would have played 6 games in 25 days (from April 5 to April 30).