(Donna McWilliam/AP Photo)

NED BERKOWITZ reports:

A long-serving Pennsylvania Democrat has joined Republican colleagues to ask Defense Secretary Chuck Hagel to overturn the "indefensible" decision by the military to designate the Fort Hood massacre "workplace violence" rather than terrorism.

"This designation has since resulted in an embarrassing lack of care and treatment by our military for the victims and their families," said Rep. Chaka Fattah (D-Penn.), Rep. Thomas Rooney (R-Fla.) and Rep. Frank Wolf (R-Virg.) in a later dated May 6 and obtained by ABC News.

DOCUMENT: Letter to Defense Secretary Hagel

In the letter, the trio of lawmakers blame "considerations of 'political correctness'" not only for the "workplace violence" designation, but for allowing the attack to unfold in the first place.

Fattah's entrance into the controversy comes after Republicans in Congress have generally taken the lead in pressing the White House for answers about the victims' treatment, as chronicled in an ABC News investigation.

READ: Fort Hood Hero Says President Obama 'Betrayed' Her, Other Victims

In a statement to ABC News, Congressman Wolf said, "I believe more members of Congress, on both sides of the aisle, are coming to realize how poorly the Obama Administration has treated families of the victims and the survivors of the Ft. Hood terrorist attack over the last four years."

Thirteen people were killed, including a pregnant soldier, and 32 others wounded in the Nov. 5, 2009 rampage at the Army base in Killeen, Texas.

The new letter alleges "political sensitivities" regarding the alleged shooter, Maj. Nidal Hasan's "extremist" Muslim beliefs prevented the FBI from properly investigating Hasan before the attack, despite evidence he was in communication with high-profile al Qaeda cleric Anwar al-Awlaki.

Since the attack, the military has denied the victims a Purple Heart and certain combat-related benefits by calling the deadly incident "workplace violence."

A Pentagon position paper, obtained by ABC News in March, said the military has treated the Fort Hood victims well, and that giving them the Purple Heart could "irrevocably alter the fundamental character of this time-honored decoration" and "undermine the prosecution of Hasan by materially and directly compromising Hasan's ability to receive a fair trial."

READ: No Purple Heart for Fort Hood Victims, Pentagon Says

After numerous delays, that trial is now set to begin on May 29.