WASHINGTON, Jan. 6 -- Some of the most popular US national parks can use entrance fees to fund basic maintenance operations amid the White House's decision to keep the parks open but understaffed during the ongoing partial government shutdown, US media reported Sunday.

Citing an order from the US Department of the Interior on Saturday, The Washington Post reported that those parks are unprecedentedly permitted to tap into entrance fees to pay for additional staff brought to clean restrooms, collect trash and patrol the parks and open areas.

Those operations have ceased, and staffers in charge of the work reduced, as a lapse in appropriations for the National Park Service (NPS), which is affiliated to the Interior Department, continued into the 16th day of the shutdown.

"We are taking this extraordinary step to ensure that parks are protected, and that visitors can continue to access parks with limited basic services," National Park Service Deputy Director Daniel Smith was quoted by the Post as saying.

The NPS has not decided how many parks are able to take the measure, the Post reported. According to information on NPS's website, 115 of the total 418 national parks collect entrance fees.

Critics, including park advocates and congressional Democrats, have challenged the legality of the move, since the fees collected at the parks, as stipulated in the Federal Lands Recreation Enhancement Act, are supposed to be spent on "repair, maintenance, and facility enhancement related directly to visitor enjoyment, visitor access, and health and safety" and other purposes, rather than on operations bolstered by congressional appropriations.

At least seven people have died in national parks across the country since the federal budget impasse triggered the shutdown on Dec. 22, raising concerns that the government's decision to keep the parks open while underfunded is both risky and unsustainable. Previous administrations had closed the national parks during times of extended government shutdown due to safety considerations.

The Post cited official estimate as saying that as many as 16,000 of the NPS's 20,000-person winter workforce is furloughed.

With no end in sight, the partial government shutdown has affected nine cabinet-level departments and dozens of agencies, forcing about 420,000 federal employees whose jobs are deemed essential to work without pay, while some 380,000 others were asked to take unpaid leave.