A powerful Republican congressman is skirmishing again with the National Park Service over the Occupy D.C. protesters who have been camping out in McPherson Square since Oct. 1.

Rep. Darrell Issa (R-Calif.), the chairman of the House Committee on Oversight and Government Reform, which oversees the District, said in a letter to Interior Secretary Ken Salazar on Tuesday that the Park Service had been "unresponsive" to the "overwhelming majority" of the committee's requests for information regarding the ongoing protest at the federally owned park.

Issa's committee launched an investigation last month into whether the Occupy protesters are camping on federal parkland illegally and has asked the Park Service for a number of materials, including a written explanation of the difference between a "24-hour vigil" and camping out.

Issa is also seeking records of all communications among the Park Service, the Interior Department and the White House as well as District government and the protesters themselves. The committee also wants to know whether the Park Service plans to stop protesters from camping in the square.

Issa said that has not received the materials he asked for and that if they aren't submitted by Jan. 24 the committee would consider its options to compel Interior to hand them over. “The Committee may need to consider the use of compulsory processes to obtain this information," Issa wrote.

In a letter to Issa dated Friday, Peggy O'Dell, the deputy director of operations for the Park Service, wrote that Americans’ right to demonstrate on federal land in the nation’s capital was supported by case law dating back decades. The Park Service had determined that the group in McPherson has a right to demonstrate without a permit and to erect temporary structures to meet their logistical and supportive needs, she wrote. U.S. Park Police monitor the camps round-the-clock and had made 61 arrests so far, for such offenses as assault, threat and disorderly conduct.

“If the protest continues, NPS will continue to exercise its discretion and take a common sense approach as it works to respect First Amendment rights and enforce NPS rules as well as other laws," O'Dell wrote. She also said that of the $400,000 in federal stimulus money that had been used to spruce up the square last year -- another of Issa's concerns -- only $8,000 was spent for sod.

"First Amendment activities...often come with a measure of wear and tear on our national parks," she wrote.

Adam Fetcher, a spokesman for Salazar, said Tuesday that the department had provided a "thorough" response to the chairman’s letter, which detailed the "firm commitment" of the Park Service to protect their resources and enforce laws "while respecting Americans' First Amendment rights."

"We will continue to work with the committee to provide information that is responsive to this request,” Fetcher said.