Visitors to the nation's capital this week may have been disappointed to learn many of the city's most famous monuments are temporarily closed to the public - a consequence, lawmakers have said, of the federal government shutdown.

But, spurred by a high-profile visit to the World War II memorial by veterans, some conservative members of Congress are questioning the National Park Service's decision to close the sites to the general public, as officials associated with the park service defend it.

Today, the chairman of the House Oversight Committee announced that he has requested additional information from the park service outlining its position.

"The committee is concerned with NPS's allocation of resources during this time of lapsed funding," Rep. Darrell Issa, R-Calif., wrote in a letter to National Park Service director Jonathan Jarvis. "Numerous media outlets have reported that NPS has erected barricades to keep people from entering the National World War II Memorial and other monuments."

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On Tuesday and Wednesday, busloads of elderly veterans with the "Honor Flights" non-profit group arrived at the World War II memorial to find it closed with bike-rack style barricades. However, a handful of park police at the site did not interfere when the vets and volunteers entered anyway, as a circus of media and lawmakers watched. Later, the Park Service declared that the Honor Flights, or any veteran, could enter the memorial freely under First Amendment protection.

Issa is the second committee chairman to formally inquire with park officials. On Wednesday, Rep. Doc Hastings, R-Wash., of the House Natural Resources Committee questioned why some less popular locales remained open and requested the service "take steps as necessary to keep and not destroy documents related to the decision this week to restrict public access."

"There were the same number of park police along the National Mall when it was open last week as there are now when it is closed," Hastings wrote. "In fact, on Tuesday, when barricades were first erected and areas closed down, there were even more police than on a typical day when it is open. It is further proof that these closures have nothing to do with the shutdown are simply about the Obama administration playing politics."

Hastings added that some open-air sites can be unstaffed for up to 10 hours a day.

"Congressman Hastings is incorrect in that regard," director Jarvis fired back on C-SPAN this morning. "We run a 24-hour-a-day, seven-day-a-week, 365-day-a-year operation on the National Mall. Under normal circumstances, I would have 300 employees working on the National Mall and I currently have seven."

That there are the same number of U.S. Park Police on the National Mall now as before the shutdown began is true, according to the U.S. Park Police officers' union. At any given time, there are two police officers on duty at each of the big three tourist sites on the National Mall: the Lincoln Memorial, the Jefferson Memorial and the Washington Monument. They are joined by a smattering of roaming officers among the less-popular sites and smaller parks.

While those officers have been deemed essential for security reasons by the park police and remained on duty through the shutdown, their numbers saw a temporary boost Tuesday as the barricades were erected, according to the union.

But, officials said, that small law enforcement footprint was dwarfed in comparison to the larger number of park service employees that would normally be on duty. For example, before the shutdown there was a large contingent of park rangers on the clock, a separate entity from the park police.

Almost all maintenance staff and other supplemental employees were also sent home without pay.

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The head of the US Park Police officers' union told ABC News that safety and health concerns seemed to outweigh the inconvenience to tourism.

"My understanding is that one of the reasons these areas are closed is because maintenance people aren't going to be there, [park rangers] aren't going to be there to give information about these areas," union chair Ian Glick said. "Maintenance also deals with trash pickup. The memorials will become very messy. We've had people slip and fall because they don't know where the wheelchair ramps are. Park rangers generally direct them."

Glick pointed out that, in addition to dealing with tourists, park rangers also act as extra eyes and ears for law enforcement. To compare police presence to overall staffing, he said, was "talking about apples and bananas. They aren't even the same shape."

"Simply from an operational and not security perspective, I think it makes sense [to close the sites]," Glick added. "Visitors leave trash and I know people will say, 'Oh a couple of soda cans being left around.' No, that's not the case. We get tons of trash. Lots of trash. If it's not picked up, it will invite rats."