the house may refuse to seat a member-elect only if he or she
a. has engaged in disorderly behavior
b. has violated the code of ethics passed by the house in 1977
c. does not meet constitutional standards of age, citizenship, and residency
d. does not meet informal standards set by two-thirds of the members
b.
I think this is a Constitutional issue.
http://www.senate.gov/civics/constitution_item/constitution.htm