"We will make it mandatory," Mary Mayhew, Maine's commissioner of health and human services, said at a news conference. Hours earlier the nurse, Kaci Hickox, vowed to defy the order keeping her at home while she is monitored for Ebola symptoms.
"There is no medical evidence that has been proposed or put forward by anyone that says Kaci is a risk," Hickox's attorney, Steven J. Hyman, told the Los Angeles Times.
In an interview with NBC's "Today" show, Hickox remained defiant.
"If the restrictions placed on me by the state of Maine are not lifted by Thursday morning, I will go to court to fight for my freedom," she said.
Hickox spoke by Skype from Fort Kent, Maine, where she has been told to stay until the 21-day observation period ends next month. She says she remains symptom-free and therefore not a threat to anyone.
The 33-year-old nurse has become the face of a nationwide debate over treatment of healthcare workers returning from West Africa. The controversy erupted Friday when New York and New Jersey announced mandatory quarantines for such workers arriving in those states.
Hickox arrived at Newark Liberty International Airport in New Jersey that afternoon and was swiftly placed in isolation in a tent at University Hospital. Hickox has denied New Jersey Gov. Chris Christie's assertion that she was running a fever.
On Monday, Christie let Hickox go home to Maine. By then, Maine had announced a similar quarantine program and said Hickox had to stay inside until the 21-day incubation period for Ebola had ended.
"Staying at home for the duration of this 21-day period - Nov. 10 being her last day - does not seem like a burdensome request to ask," Mayhew said. She said the measure was taken "out of an abundance of caution."
Asked what possible risk Hickox could pose to the public if she were not symptomatic, Mayhew said, "There are other cases where individuals have not tested positive … and quickly developed symptoms when they were out in public."
That could have been a reference to Amber Vinson, a Dallas nurse who had a slight fever when she boarded a jet in Cleveland a few days after an Ebola patient she had helped care for died.
That patient, Dr. Craig Spencer, is hospitalized in stable condition. Healthcare officials in New York say he was not symptomatic when he was out in public.
Several states, including California, now have quarantine systems to varying degrees as a result of the Ebola outbreak in West Africa and the handful of cases in this country.
"I remain appalled by these home quarantine policies that have been forced upon me, even though I am in perfectly good health and am feeling strong," Hickox told NBC. "I have been, this entire time, completely symptom-free. I am thankful to be out of the tent in Newark, but I find myself in yet another prison in a different environment."
"While we certainly respect the rights of one individual, we must be vigilant in protecting 1.3 million Mainers, as well as anyone who visits our great state," he said.
But Maine could have problems enforcing the quarantine, said Paul Millus, a New York attorney and civil rights litigator.
"I never claimed to be a medical expert, but I do claim to be fairly good at common sense," he said Wednesday. "And common sense is that if you've been a healthcare worker who's been directly exposed to the virus, and you come back to the U.S., you should quarantine for 21 days."