Walker Zimmerman also scored as FC Dallas (8-3-6) picked up its second consecutive draw pulled into a first-place tie with Real Salt Lake and Portland atop the Western Conference.
Aaron Wheeler had put the Union ahead in the 87th minute. He was inserted as a substitute just 8 minutes earlier and got his first career goal. Amobi Okugo also scored for the Union (7-5-5) while Sheanon Williams added two assists.
The Union extended their unbeaten streak to 2-0-2, narrowly missing a chance to tie a franchise mark with a third consecutive victory.
FC Dallas went down a man in the 68th minute when Je-Vaughn Watson picked up his second yellow card and was ejected.