Fannie Mae said it could change pricing and other terms under purchase agreements and mortgage-backed securities contracts with lenders, according to an alert Tuesday.

New rules could affect lenders with large inventories of outstanding repurchase requests.

For any contracts and agreements entered into on or after May 1, Fannie said it reserves the right to change pricing "one or more times" during the term. It would provide the lender with a written notice before any changes are made, and if the lender disagrees with new terms, either party could cancel the arrangement.

Fannie purchased $68.3 billion in mortgages during March, a 54% increase from one year ago and the highest monthly total since October 2010.

Some lenders have already begun new negotiations.

The mortgage subsidiary for PHH Corp. (PHH) renewed its master agreement with Fannie amending a $1 billion sale commitment to the government-sponsored enterprise, according to a financial filing Tuesday.

PHH will lose its contract if the company's net worth falls below $1 billion. Its net worth currently stands at about $1.5 billion.

Fannie also built in new stipulations for repurchase requests. As of May 1, PHH could have its contract with the GSE severed if 30% of its buyback requests went without action for more than 180 days.

The lender is expected to shrink this inventory. As of June 1, severely aged outstanding repurchase requests cannot exceed 10% of the total, and by July 1, it must drop to below 5%, according to the PHH filing.

After July, no buyback requests can be outstanding for more than 270 days or PHH could lose its contract.

Disagreements on rep and warranty issues already cost Bank of America (BAC) its business agreement with Fannie in the first quarter.

PHH warned investors the GSE was vital to its mortgage operation.

"As a Fannie Mae approved seller and servicer, PHH Mortgage sells a substantial portion of the mortgage loans it originates to Fannie Mae and generally retains mortgage servicing rights in respect of such loans," PHH said in its filing.

Profits at its mortgage department more than doubled from one year ago.