A member of a British parliamentary committee studying cultural funding in these economically straitened times "drily suggested" that Gustav Mahler "shouldn't have
written works that require so many musicians," The Observer's Fiona Maddocks reports as she surveys performances in 2010, the sesquicentennial of Mahler's birth, and anticipates programming in 2011, the centennial of the composer's death:http://www.guardian.co.uk/culture/2010/dec/12/classical-music-2010-review-maddocks
Scores for large forces were endemic in Mahler's time. Other offenders include Anton Bruckner (any of the symphonies from No. 2 onward), Richard Strauss ("Ein Heldenleben," "Alpine Symphony"), Maurice Ravel ("Daphnis et Chloë"), Claude Debussy ("La Mer"), Arnold Schoenberg ("Gurrelieder"), Igor Stravinsky ("The Rite of Spring") . . . the list goes on.
For a much shorter list, name the orchestral masterpieces from the late-19th and early 20th centuries that do not require what a number-cruncher would call excessive performing personnel.