The Senate Veterans’ Affairs Committee seems poised to advance a popular bipartisan bill extending disability benefits to Vietnam veterans who claim they were exposed to Agent Orange. But Department of Veterans Affairs officials said Wednesday the agency opposes the measure.

Lawmakers on both sides of the aisle expressed strong support for the legislation at a hearing Wednesday, questioning whether the VA adequately considers applications from vets who served in ocean vessels claiming exposure.

The “blue water” bill would extend the presumption that Navy veterans who served in open waters during the Vietnam War were exposed to herbicides like Agent Orange. Veterans who served on inland water or who set foot on land during the war already benefit from the presumption.

The change means that veterans whose open-water ships came within 12 nautical miles of the Vietnam coastline would no longer have to prove their conditions are directly related to their service in order to qualify for disability benefits, which veterans groups say is frequently impossible. The bill passed the House unanimously in June.

VA officials at the hearing cited a lack of scientific evidence that blue-water veterans were indeed exposed. A key study on Australian ships that advocates highlight doesn’t account for the differences in distillation processes for American ships, said Ralph Erickson, VA chief consultant for post-deployment health. Both types of ship distilled water for the sailors to use, but Australian ships did so closer to shore, making it more likely that the service members would be exposed to herbicides.

“In summary, we oppose this bill because the science is not there,” said Paul Lawrence, the VA’s undersecretary of benefits. “And what we do depends on science.”

Many veterans say their claims are automatically rejected if they did not set foot on land. But Lawrence said a process exists for blue-water veterans to be considered for disability coverage.

“You wouldn’t have had a vote that you had so strong out of the House if many people believed that,” West Virginia Democrat Joe Manchin III told Lawrence. “You wouldn’t have so many people supporting it in the Senate if the constituents weren’t saying, listen, we’re just not being treated fairly.”

The expansion would be funded by increasing the fees veterans must pay for a home loan.

“I assume this bill is going to pass probably if it comes out and comes to the floor. I don’t know anybody that would be against it,” Manchin added. “Because we all have constituents who have been rejected without a fair evaluation. That’s about it in a nutshell.”

Chairman Johnny Isakson of Georgia vowed to do more to do on these issues.

“This is not the end,” he said. “This is the beginning.”