My company is adding imputed income to my checks for my domestic partner, even tho I can claim her as my dependant on my tax returns. What do I do? HR isn't helping.

I've talked to HR about removing the imputed income from my checks, as it has caused me to make less at the end of the day. They weren't doing this at first now they are, and I noticed a major difference in take home pay. What do I do? My HR department is completely clueless on the subject.