The Obama administration extended a December deadline by two days, amid a surge in enrollment. Above, Alberto Abin walks out of the UniVista Insurance company office after shopping for a health plan under the Affordable Care Act, also known as Obamacare, on Dec. 15, 2015 in Miami, Florida. Joe Raedle/Getty Images

The White House announced Tuesday it would extend a key deadline for Obamacare enrollment, despite previous vows not to do so and amid claims of troubles with the website, Customers who wanted coverage starting Jan. 1, 2016 initially were required to sign up by Tuesday at the latest, but the Department of Health and Human Services extended that to 11:59 p.m. PST Thursday, citing "unprecedented demand at and our Marketplace Call Center."

The extension came amid a swell of visits to the federal website and those of state marketplaces, including New York and California, before the Dec. 15 deadline. “During this period of unprecedented traffic, remained open for business and ready to sign people up for 2016 health plans,” Lori Lodes, a spokeswoman for Health and Human Services, said in a statement.

The move calls into question whether the administration will adhere to future limitations it has imposed, such as refusing to open a special enrollment period after Jan. 31, 2016 for people who failed to sign up during official open enrollment, which began Nov. 1 and ends Jan. 31, 2016.

Federal officials said in early December that they would not relax the rules for those who failed to sign up for Obamacare during open enrollment period. The special enrollment period, typically reserved for those with major life changes like getting married or losing existing coverage such as an employer-sponsored plan, but in the spring of 2015, the administration allowed people who missed a Feb. 15 deadline to sign up for healthcare afterwards, especially after many people realized only upon filing taxes, due in April, that they had to have insurance or pay a penalty. This year, the government has said it will not be so lenient.

"A Special Enrollment Period around the April 15 tax filing deadline will not be offered this year," Kevin Counihan, the chief executive of, wrote in a blog post Dec. 7. "If you don’t enroll by then, you could have to wait another year to get coverage and may have to pay the fee when you file your 2016 income taxes," he added. Under the penalty, individuals without health insurance have to pay a fee of $695 or 2.5 percent of their annual income, whichever is higher.

Some insurers and analysts have suggested that the 2015 special enrollment period pushed up healthcare costs by allowing sicker people to sign up. When UnitedHealth said in November that it was considering dropping out of the exchanges created under Obamacare, it pointed to the special enrollment period as allowing people to sign up when they become sick, causing the company to lose money. "These have been strong users of services," UnitedHealth Group CEO Stephen Hemsley said of special enrollees.

The Obamacare call center received more than 1 million phone calls on Monday alone, while the website received a record high of 185,000 simultaneous visitors that night, the Department of Health and Human Services said.