Financial talk

Hi, I have recently been given a pay rise which was part cost of living and part performance related. The performance related put me as being satisfactory/improving but I have grafted for the company since returning from maternity leave in October 2007. I have 3 years of experience in my role and have met all my objectives during the last financial year. Basically I want to challenge the decision but don't want to be confrontational and burn all my bridges. Can anyone help or point me in the right direction ie: useful sample letters/websites. I can't blow it as I need the job, but I do have to challenge it as it is so unfair and down to the subjectivity of my boss who thinks that women should stay home when they've had kids. Thanks for any help with this.