After nearly a year of arguments between the Homeland Security Department and its House authorizing committee over an initiative to use satellites for domestic surveillance imaging purposes, committee leadership is trying to hit the program in the pocketbook.

In a letter to committee and subcommittee chairs in the House Intelligence and Appropriations committees, the Homeland members said the National Applications Office may run afoul of the Posse Comitatus Act, a statute dating back to the post-Reconstruction era that keeps the military out of regular law enforcement activities.

The authors said the issue is the NAO’s planned use of military satellites “for surveillance of American citizens inside of the United States for law enforcement and other purposes,” and accused DHS of working outside of the law.

“Having been burned on the Terrorist Surveillance Program and knowing of this administration’s disdain for obeying the laws Congress passes, we need to be extraordinarily careful,” wrote House Homeland Chairman Bennie Thompson , D-Miss., and Jane Harman , D-Calif., chairwoman of the Intelligence, Information Sharing and Terrorism Subcommittee. Later, they added, “We strongly believe that any funding is premature and risks further eroding the privacy and civil liberties rights of all Americans.”

DHS has countered that the letter shows that the lawmakers don’t understand the NAO, despite “numerous briefings” by Secretary Michael Chertoff and other staff.

“The purpose of the NAO is not to expand existing legal authorities,” DHS spokeswoman Laura Keehner said. “It is to allow the government to better and more efficiently prioritize the use of scarce resources in support of major disasters, homeland security efforts and, in the future, law enforcement. We have said repeatedly that we will brief Congress before moving to support law enforcement.”

Keehner said the letter also errs in its application of the Posse Comitatus Act.

“For one thing, these satellites are not exclusively for military use,” she said. “But in any event, the [act] and other laws permit indirect military support to law enforcement, particularly through equipment.”

The NAO has been a sore spot between DHS and the committee since its operational start date appeared in media reports — before congressmen were consulted on it.

The office, which is still in the planning stages, would oversee satellites capable of producing high-resolution images in real-time, along with other remote sensing technology. DHS says the technology has existed for decades; they’re just providing organization so it’s used more efficiently. Currently, a central conflict between Congress and the department is when the office would open for operations.

At first, the NAO will monitor only natural or man-made disasters, as well as high-threat events, DHS said. After legal and civil liberties issues are addressed, the office’s images will be used for law enforcement purposes like border control and emergency response. House Homeland members, however, have said that until that legal framework is in place, the office should not undertake any operations.

In their latest letter, sent Thursday, Thompson and Harman questioned why DHS needs the NAO at all.

“By the department’s own admission, existing authorities are adequate to permit emergency use of military satellites in extreme weather situations or to protect large outdoor mass gatherings like the Super Bowl or the World Series,” they wrote. “Thus, the question becomes what unmet law enforcement purposes or needs would the creation of the NAO serve. We have asked the department this question repeatedly and they have been unable to respond.”