CAPE ELIZABETH Maine (Reuters) - A nurse who treated Ebola patients in Sierra Leone but has tested negative for the virus went for a bike ride on Thursday, defying Maine's order that she be quarantined in her home and setting up a legal collision with Governor Paul LePage. Attorneys for Kaci Hickox, 33, said they had not yet been served with a court order to enforce the 21-day quarantine - matching the virus's maximum incubation period - but remained prepared to fight such an order if necessary. The quarantine showdown between Hickox and Maine has become the focal point of a struggle between several U.S. states opting for stringent measures to guard against Ebola and a federal government wary of discouraging potential medical volunteers. Mandatory quarantines ordered by some U.S. states on doctors and nurses returning from West Africa's Ebola outbreak are creating a "chilling effect" on Doctors Without Borders operations there, the humanitarian group said on Thursday. LePage's office said negotiations with Hickox, who worked with Doctors Without Borders in Sierra Leone, "have failed despite repeated efforts by state officials" and that he would "exercise the full extent of his authority allowable by law." Hickox left her home in the small Maine town of Fort Kent, along the Canadian border, and television news images showed her taking a morning bicycle ride with her boyfriend, Ted Wilbur. Hickox has given the New England state a deadline of Thursday to lift an order that she remain at home until Nov. 10, or she will go to court. “It’s a beautiful day for a bike ride,” said Hickox, wearing a helmet and other bike gear as she headed out for her 3-mile (5-km) ride while police stationed outside her house stood by without trying to stop her, according to local media. LePage's office said he was open to an arrangement in which she could go for walks, runs or bike rides but not go into public places or come within 3 feet (1 meter) of other people. “I was ready and willing - and remain ready and willing - to reasonably address the needs of healthcare workers meeting guidelines to assure the public health is protected,” said LePage, a Republican locked in a tough three-way re-election battle. President Barack Obama, who has criticized mandatory quarantine policies imposed by some states for returning medical workers like Hickox, flew to Maine on Thursday to campaign in the town of Cape Elizabeth for Democratic candidates, including Mike Michaud, who is trying to unseat LePage in Tuesday's midterm elections. Asked for comment on Hickox's situation, White House spokesman Josh Earnest told reporters aboard Air Force One en route to Maine that U.S. Centers for Disease Control and Prevention officials have been in regular touch with the health authorities in the state. "Ultimately, it is their decision," said Earnest, adding that Obama had no plans to see Hickox while in Maine. Cape Elizabeth is at the opposite end of the state, on its southeastern coast. One of Hickox's attorneys, Norman Siegel, defended his client's decision to go for a bike ride but noted that she avoided the center of town so as not to “freak people out.” “Since there’s no court order, she can be out in public,” Siegel said. “Even if people disagree with her position, I would hope they respect the fact that she’s taking into account the fear, which is based on misinformation about the way the disease is transmitted.” Medical professionals say Ebola is difficult to catch and is spread through direct contact with bodily fluids from an infected person and is not transmitted by asymptomatic people. Ebola is not airborne. U.S. concern about the disease is high even though there is only one person in the country currently being treated for it, a New York doctor, Craig Spencer, who cared for patients in West Africa. Spencer, 33, remains in serious but stable condition, New York's Bellevue Hospital said on Thursday. Hickox tested negative for Ebola after returning from Sierra Leone, one of the three impoverished countries at the heart of the outbreak that has killed about 5,000 people there. She previously blasted New Jersey Governor Chris Christie after she was taken from Newark's airport and put in isolation in a tent before being driven to Maine to spend the rest of her 21-day quarantine at home. Such treatment of returning medics is affecting those still in West Africa, said Sophie Delaunay, executive director of Doctors Without Borders. "There is rising anxiety and confusion among MSF staff members in the field over what they may face when they return home upon completion of their assignments in West Africa," said Delaunay in a statement emailed to Reuters. Doctors Without Borders is also known by its French name, Médecins Sans Frontières, or MSF. With elections coming Tuesday, Republicans aiming to take full control of the U.S. Congress have made criticism of Obama's response to Ebola - which they call inept and too weak - a part of their campaign message. Some U.S. states have imposed automatic, 21-day quarantines on doctors and nurses returning from treating Ebola patients in Liberia, Sierra Leone and Guinea. Obama and other critics say such steps may discourage American doctors and nurses who are desperately needed there from volunteering. New York City and state officials on Thursday announced a program to encourage healthcare professionals to work in West Africa, an effort to deflect criticism of the state's mandatory quarantine. The program will provide financial incentives and employment protections similar to the benefits and rights provided to military reservists, New York Governor Andrew Cuomo and New York City Mayor Bill de Blasio said jointly.