Rep. Darrell Issa, shown in June, is asking the Interior Department why Occupy protesters have been allowed to remain in McPherson Square. (Stephen Morton/BLOOMBERG)

The group plans to visit congressional offices, including those of Rep. Darrell Issa (R-Calif.) and Senate Majority Leader Harry Reid (D-Nev.), according to the group’s Web site.

In a letter dated Monday, Issa asked Interior Secretary Ken Salazar why protesters have been allowed to remain in McPherson Square despite a National Park Service ban on overnight camping.

The Republican said he objected to protesters damaging grass and landscaping in the park after $400,000 in stimulus funds were spent to upgrade them. He’s asking the department to detail any communication it had with the White House about the downtown protests.

Del. Eleanor Holmes Norton (D-D.C.), who has been supportive of the protesters’ goals, said Issa’s letter means that they will have to be “more careful.”

“They have been trying to clean up after themselves, and we hope we are able to keep this peaceful as it has been up to now,” Norton said.

When asked whether Occupy D.C. should be allowed to continue to camp in McPherson Square, Norton replied, “I think they’ve got to be very careful.”

“We don’t want the same thing to happen here as has happened in other cities,” said Norton, referring to police raids on other Occupy encampments. “Everybody supports them, the [D.C.] Council supports them, we all support them. We support their underlying message, we just want them to be careful about the rights of others while they get their message out.”

Adam Fetcher, Salazar’s press secretary, said in a statement that the agency was reviewing Issa’s letter and will “respond accordingly.”

“The National Park Service and U.S. Park Police are firmly committed to upholding Americans’ First Amendment rights while also enforcing our nation’s laws, guarding public safety, and protecting the resources with which we are entrusted,” Fetcher said. “To that end, the U.S. Park Police have been working closely with the District of Columbia, the Metropolitan Police Department, the DC Department of Health and others to ensure that demonstrations associated with the ‘Occupy’ movement are conducted safely and in compliance with the law.”

The Post’s Tim Craig is following the protesters on the Hill. Follow his tweets for the latest updates:

View Photo Gallery: A look back at notable Occupy D.C. incidents.

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This post has been updated since it was first published.