Marriage among Karaite Jews is not unlike that among Rabbanites. One notable difference being there is no restriction on polygyny within Karaite Judaism. This is increasingly rare in the modern day, however, and the ability of the husband to take other wives hinged, not only on his ability to equally fulfill his duties to them, but also the acceptance of the act by the primary wife. The primary wife is well within her rights to include an anti-polygamy clause in their betrothal contract.[52]

(http://www.autoadmit.com/thread.php?thread_id=5724966&forum_id=2E#48930546)