Two members of Congress left some information in the dark when filling out their personal financial disclosure forms, which were made public last week.

According to ethics rules, if a member of Congress sits on the board of directors at a nonprofit, he or she is supposed to disclose the position. But at least two representatives—Corrine Brown, D-Fla., and Ander Crenshaw, R-Fla.—have failed to do so. The lawmakers' positions were discovered while researching lobbying reports, where lobbyists report honorary gifts to charities tied to members of Congress. There could be many more members of Congress making the same ...