The quest for answers for thousands of veterans sickened -- in some cases terminally -- by contaminated water at Camp Lejuene has been stymied by a federal agency that refuses to hand over key documents, attorneys from Yale Law School charged Wednesday.

The Veterans Legal Services Clinic at Yale Law School filed a Freedom of Information Act (FOIA) lawsuit in federal court Wednesday against the Department of Veterans Affairs for allegedly withholding information on a group of "experts" denying claims for scores of veterans exposed to cancer-causing chemicals at the North Carolina base.

The suit, which represents two veterans groups, seeks to compel the VA to respond to a December 2015 FOIA request about the SME program -- an anonymous group of "subject matter experts" who render medical opinions on the veterans exposed to toxic water at Camp Lejuene  between 1953 and 1987.  

"The SME program remains a black box."

- Rory Minnis, Yale Law student and former Marine

Since the program's launch three years ago, the rate of Camp Lejeune toxic water disability claims being approved has dropped from approximately 25 percent to 8 percent, according to VA statistics. Advocates for veterans want to know who the purported experts passing judgment on the claims are, and how they arrive at their conclusions.

"The VA has yet to provide an official response to the request or even to provide a single responsive record," Rory Minnis, a former Marine and second-year Yale law student, told reporters Wednesday.

"For several years now, Camp Lejeune advocates, individual veterans, and the media have repeatedly requested informationon the SMEs’ credentials, training, methodology, and programmechanics. Yet, the SME program remains a black box," said Minnis. "The VA’s failure to respond to our clients’ FOIA request is just the latest instance in a long pattern of foot-dragging and misdirection in response to inquiries about the SME program."

Between 1953 and 1987, nearly 1 million veterans, their families and civilian employees at Camp Lejeune were exposed to drinking and bathing water contaminated with dry cleaning chemicals, degreasers and a host of other toxins. Many base residents developed illnesses -- including rare cancers -- and disabilities in the aftermath.

According to the Agency for Toxic Substances and Disease Registry, "past exposures from the 1950s through February 1985 to trichloroethylene (TCE), tetrachloroethylene (PCE), vinyl chloride, and other contaminants in the drinking water at the Camp Lejeune likely increased the risk of cancers (kidney, multiple myeloma, leukemias, and others), adverse birth outcomes, and other adverse health effects of residents (including infants and children), civilian workers, Marines and Naval personnel at Camp Lejeune."

Victims claim the U.S. Marine Corps hid knowledge of the problem for years and did not warn people their health might be at risk.

One SME report used to deny a Camp Lejeune veteran’s claim featured language cut and pasted from Wikipedia, Minnis said Wednesday. Another rejected the judgment of the veteran’s treating VA doctor amd a third falsely claimed – against well-established medical consensus – that there was no causal link between trichloroethylene, a known carcinogen, and kidney cancer, according to the legal team at Yale.

The goal of the lawsuit -- which represents The Few, The Proud, The Forgotten and Vietnam Veterans of America -- is to seek records on how the SME program is structured, staffed, and operated.

The VA told FoxNews.com in December that it established the SME program in 2012 to "complete Camp Lejeune medical opinions based on scientific studies and to bring additional occupational exposure science into the claims review process."

"The selected SMEs are clinicians trained in occupational medicine, environmental medicine, and toxicology," Walinda West, a Veterans Affairs spokeswoman, had said. "Additional training is provided following their selection as an SME at the Regional office Louisville, Ky."

West described the clinicians as "highly experienced professionals" who have been "directly or indirectly involved with care and/or assessment of our Veterans at VA Medical Centers."

The VA's response -- or lack thereof -- has sparked lawmakers, like Sen. Richard Blumenthal, D-Conn., to press for greater transparency on the credentials and conclusions reached by the unidentified group of clinicians. 

"The VA's lack of response to these brave men and woman is utterly irreposnable and unacceptable," Blumenthal, D-Conn., said on a conference call Wednesday with reporters.

Retired Master Sgt. Jerry Ensminger, founder of The Few, The Proud, The Forgotten -- one of the groups seeking information -- lived on the base with his family in 1975. Ensminger's young daughter, Janey, was diagnosed with leukemia at age 6 and died when she was 9. After learning about the water contamination in a local news report years after Janey's death, Ensminger said he made it his mission to press the government for accountability.

On the same conference call Wednesday, Ensminger claimed Camp Lejeune veterans are the "only veterans who have been subjected to this so-called SME program." 

"Their modus operandi is delay and deny until they die," added Rick Weidman, executive director for policy and government affairs for Vietnam Veterans of America. 

"There is no definition of who the subject matter experts are," said Weidman. "It's absolutely unacceptable in a democracy to hide behind anonymity."

Cristina Corbin is a reporter for FoxNews.com. Follow her on Twitter @CristinaCorbin.