Richard Foster, in Money, Sex & Power (the whole section on the correct use of power as a Christian is very interesting) states,

"How do we serve others in the world? We serve them by a firm refusal to allow them to misuse and abuse us. To allow people to walk over us as one would a doormat is not service, but subservience. It is not healthy for us or for others. Service must not be identified with a false modesty or a Caspar Milquetoast personality. On the contrary, service resonates well with forthrightness and courageous action.

Therefore, if others try to walk over us and take advantage of our serving spirit, we stand up to the abuse. Our concern is not to defend 'our rights', for we have already given those to God. Firmly, we press others to respect all people - including us - as fully human. The issues can be many and varied - low salary, heavy workload, lack of advancement - the resolve is always the same: never to be 'thing-a-fied.' "