A bipartisan group of lawmakers called for more modifications to the Home Affordable Refinance Program (HARP) Wednesday in a public letter addressing federal officials.

Sen. Barbara Boxer (D-California) and Sen. Johnny Isakson (R-Georgia) announced the letter in a statement with eight of their colleagues from across the aisle.

The senators aimed their call to action at Treasury Secretary Timothy Geithner, HUD Secretary Shaun Donovan, National Economic Council Director Gene Sperling, and Federal Housing Finance Agency (FHFA) Acting Director Edward DeMarco – past recipients of another public letter submitted by a number of the same senators even before the recent HARP expansion.

“As you prepare the final rules for the announced changes, we urge you to apply the streamlined process and reduced costs as broadly as possible, and to include all responsible

homeowners no matter what their level of equity,” the letter said.

Boxer, Isakson, and other lawmakers called for the FHFA and other federal regulators to lift access barriers to borrowers with higher-equity government-backed loans.

The letter argues that new modifications could benefit approximately 12 million other borrowers by allowing those with higher equity above 5 percent to refinance their loans.

Recent modifications for HARP include lifting the 125-percent loan-to-value ratio, eliminating risk-based fees for borrowers, and extending the life of the program until 2013.

“Not only is this an issue of fairness, but applying these measures to higher equity borrowers makes good business sense,” the lawmakers added.

The letter follows considerable movement for the program, frequently dubbed by others as HARP 2.0, as the FHFA prepares guidance for participating lenders and interested homeowners.

The nation’s four largest lenders – Bank of America, Citigroup, JPMorgan Chase, and Wells Fargo – recently agreed to participate in HARP, with statements largely praising the program expansion.

The senators tied newer modifications to economic growth in the letter, saying that “a single set of rules for all borrowers will simplify the process and encourage greater participation in the program.”

The FHFA will reportedly roll out guidance for lenders in November.