Reference: Fataawa wa Rasaa.il Shaykh ‘Abdur-Razzaaq ‘Afeefee – Volume 1, Page 166, Fatwa No.48
Question: What is the ruling regarding suing one another before a judge who rules according to man-made laws?
Response: As much as is possible, you should not sue one another under them (man-made laws). However, if one is unable to extract his right[s] other than via them (man-made laws), then there is no harm upon him [to do so].