Fannie Mae said that mortgage-insurance policyholders could be at risk if MGIC Investment Corp. carries out its plan to transfer capital from an underwriting unit.
"We have not approved" the proposed transaction as of Thursday, Fannie Mae said in a regulatory filing last week.
The plan presents "an increased risk that MGIC might not pay its claims in full in the future."
MGIC's talks with Fannie Mae and Freddie Mac caused the No. 1 U.S. mortgage insurer to postpone an initial transfer of $500 million originally scheduled by the end of July. Soaring claims have threatened to overwhelm capital at mortgage insurers.
MGIC proposed to move as much as $1 billion to an inactive subsidiary and use the money to write more insurance, the company said July 16.
"We remain in discussions with MGIC," Fannie Mae said.
Michael Zimmerman, a spokesman for the Milwaukee insurer, said in an e-mail that the capital transfer would allow the company "to continue to support the housing market on an uninterrupted basis by making low-down-payment loans available to consumers and would add value to the existing policyholders of MGIC."