Per Diem and Secondment Agreement

hi atty,

i was sent by our company for secondment in singapore for 4 months. i was given a secondment contract indicating that i'll be receiving 100sgd (net) per diem which i regularly recieved in my payroll account. two weeks after i returned, i was informed by our payroll dept that they will be deducting tax on my per diem. Though i know that per diem is indeed taxable, our company has not really consistently implementing the tax on per diem. in fact, two of my officemates who were also sent to singapore on the first quarter of this year were not deducted with the per diem tax. they told me that they will be implementing this new policy on per diem tax effective june 2012. i felt so decieved as i thought i'll be receiving 100SGD (net). my question is can i demand my company to honor what is stated on my secondment contract? if they insist that per diem is indeed taxable can i charge them with damages as they have put me technically in debt with my company, as i owe them 110k of per diem tax. Hope you can give a legal advice on this. thank you very much.

usual practice is if you provide receipts it shouldnt be taxable..