This plugin will allow you to restrict all TFC classes with votes or without votes.

Commands:
admin_vote_scout
admin_vote_sniper
admin_vote_soldier
admin_vote_demoman
admin_vote_medic
admin_vote_hwguy
admin_vote_pyro
admin_vote_engineer
admin_vote_spy
Will open a vote to restrict that class.

admin_scout
admin_sniper
admin_soldier
admin_demoman
admin_medic
admin_hwguy
admin_pyro
admin_engineer
admin_spy
Will restrict or enable that class.

So if your server has too many of 1 class vote restrict it or just restrict it.