Homeowners considering selling the mineral rights on their property may want to reconsider. The damage caused by “fracking” (a technique for removing natural gas from underground rock) has led Fannie Mae and Freddie Mac to re-emphasize policies prohibiting mortgages on any property that contains hazardous materials – specifically including oil and gas. The GSEs also have the right to exercise the “due-on-sale” clause, requiring immediate payment of the outstanding mortgage balance, if they discover violations of this policy.