An affidavit filed in federal court says documents were deleted from state redistricting computers last year even after lawmakers' aides were told to preserve all records.
The discovery raises the possibility that Republican officials or their lawyers could face sanctions from the panel of three federal judges overseeing the case.
A Milwaukee Journal Sentinel report says nine hard drives were given to groups suing the state. That's because there were questions about whether legislators and their attorneys had turned over all the documents they'd been ordered to provide.
The affidavit stated one of the hard drives was unreadable and appeared to have been tampered with. Others had an advanced file-deleting program installed on them.
A lawyer representing the firm that helped lawmakers with redistricting said the allegations are unproven.