For example: the Intercultural Union "luncheon"
Simon B. is correct.
additional comment: No. But if the luncheon is in honor of a person, for a charity event, or a retirement party the name of the honoree together with the event or occasion's name is capitalized.
Charlie Brown's Retirement luncheon. but, Healthy Octogenarian Club's Annual Fundraising Luncheon.
If it is part of the name or title of a specific event, then yes. Otherwise no.
We are having a luncheon for the tenth anniversary of the founding of this college.
Not capitalized, not the name of the event.
The Foobar University Tenth Anniversary Luncheon will be held on Thursday at noon.
The name of the event is "Foobar University Tenth Anniversary Luncheon", so it is capitalized.