Terry this happens a lot with Oncidiums. It's a fungus that is very common. Unsightly yes, and it can spread. Not really harmful unless you let it get totally out of control. You don't have to cut the leaf. Just give the plant lots of airflow.
Oncidiums require ample airflow over the leaves or they will get the spots. Another cause that can increase this is if misting occurs and the plants do not dry out quick enough.