Hedging will become much more expensive for Fannie Mae, Freddie Mac and the Federal Home Loan Banks than for anyone else as proposed new rules on the margining of uncleared derivatives will significantly increase the cost of trading, the GSEs warned federal regulators.GSEs regulated by the Federal Housing Finance Agency weighed in via comment letters on the rules proposed in April by the FHFA, as well as the Federal Reserve, the Farm Credit Administration, the Federal Deposit Insurance Corp. and the Office of the Comptroller of the Currency.