New margin rules for broker-dealers may trip up mortgage bankers using mortgage-backed securities to hedge their businesses, according to experts discussing various liquidity issues during last week’s Secondary Market Conference sponsored by the Mortgage Bankers Association. Fannie Mae has traditionally reserved the right to invoke margin calls if the government-sponsored enterprise needed to, even before the Treasury Practices Market Group issued new best practices on the subject, said Renee Schultz, a Fannie vice president, but this right was rarely used. When the TPMG recommendation came out, it appeared to be aimed at systemic risk. But since it was addressed to all broker-dealers, Fannie adopted it. Fannie has implemented...