Updated at 8:13 p.m. ET

The U.S. Department of Justice is siding with campground and restaurant owners in Maine who sued the state over a two-week self-quarantine policy for out-of-state visitors.

Democratic Gov. Janet Mills imposed the restriction as part the state's response to the ongoing pandemic. Several other states have imposed similar measures.

In a brief filed on behalf of Bayley's Campground in Scarborough and other plaintiffs, attorneys with the Department of Justice, including the U.S. attorney for Maine, said the government is getting involved because of its "compelling interest in protecting the public and citizens' constitutional right to be free from unjustified discrimination on the basis of state residency."

In this case, the federal attorneys said Maine has likely exceeded the Constitution's limits by discriminating between Mainers and people from out of state, with respect to the ability to patronize campgrounds and recreational vehicle parks.

The government's statement noted that the order doesn't require all nonresidents to go into quarantine. "As far as public safety goes, it is unclear why out-of-state residents may enter Maine to engage in any 'legal, business, professional, environmental permitting and insurance services,' for example, but not to patronize a campground or RV park. ... If Maine wants to prevent the spread of COVID-19, one would think it would start by preventing outsiders from attending a boardroom meeting, not from pitching a tent."

In response, Mills said in a statement she is "deeply disappointed and frankly disgusted – that the U.S Department of Justice is making a concerted effort to undermine the health of the people of Maine."

Mills pointed out that these objections "were never raised when the President and his own task force took steps to limit travel."

"Maintaining the 14-day quarantine ... has never been about anything other than protecting the health and safety of Maine people at a time when millions are expected to flock to our state from COVID-19 hot spots," Mills said. "I imagine it is for this same reason that so many other governors have enacted similar measures."

On Friday, the judge rejected a motion for a preliminary injunction against the governor's orders.

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