From Longman Business Dictionary
overstaffedo·ver·staffed /ˌəʊvəˈstɑːft◂ˌoʊvərˈstæft◂/ adjectiveadjHUMAN RESOURCES an overstaffed company, organization etc has more people working for it than it needsSYN OVERMANNEDWe were overstaffed in some areas and not as competitive as we should have been.
→ opposite understaffed —overstaffing noun [uncountableU]He cut the workforce sharply to eliminate overstaffing.