Those states are "starting to have" a "very early indication" of rising COVID-19 positivity rates, which is a "surefire sign that you've got to be really careful," Fauci told ABC News chief anchor George Stephanopoulos on "Good Morning America" Tuesday.
The director of the National Institute of Allergy and Infectious Diseases urged states to reopen in a manner consistent with the federal government's guidelines for reopening.
Watch full GMA interview with Dr. Anthony Fauci, NIH Director, National Institute of Allergy and Infectious Disease
Indiana's state-wide face mask mandate took effect on Monday.
Governor Eric Holcomb backed down on the idea of imposing fines or criminal penalties on those who don't comply with the order.
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"I think he did the right thing because you know sometimes certain laws get abused," said East Chicago resident Wayne Morris.
LaAzteca, a small family owned grocery store in Hammond, has had its own no mask, no service rule in place for a few weeks now. Signs are posted all over the doors.
While some customers are grateful for it, management said a small percentage have met it with resistance.
"I just try to explain to them 'Hey, it's not just about our well-being and my employees well-being, it's also about like the other customers well-being and your own well-being," said Javier Carrillo of La Azteca.
Meanwhile, Javier Carrillo says his store is giving out free masks to customers who don't have one.
Indiana health officials reported 561 new COVID-19 cases and 3 additional deaths Monday, just days after Holcomb dropped a mask violator penalty. The Indiana State Department of Health confirmed a total of 62,907 positive coronavirus cases in the state, including 2,709 deaths. There have been 707,791 tests conducted, with an 8.9% positivity rate.
With the positivity rate inching towards 9% and the number coronavirus cases continuing to climb in Indiana, the state has taken a number of steps, such as extending capacity limits on indoor businesses.
Some municipalities have closed down beaches frequented by those on the Illinois side of the border. But until now the issue of masks remained a recommendation only.
Lake County, Indiana issued a mandate last week
Governor Holcomb himself says he hopes to enforce compliance through education.
The statewide face mask order will apply to anyone ages 8 and older in any indoor public or business areas and at outdoor public spaces when sufficient distancing can't be maintained. The order took effect Monday.
Holcomb said his order will also require masks in schools for grades three and above for students, teachers and other employees. Holcomb said a renewed growth in the number of COVID-19 infections and hospitalizations necessitated the mask order.
Masks aren't required for people with specific medical reasons or for people who are doing strenuous physical activity. Eating and drinking is also an exception.
But the state's attorney general believes the governor has overstepped his authority in issuing a statewide face mask mandate and that only the Legislature can make violations a criminal offense. Republican Attorney General Curtis Hill issued an advisory opinion Wednesday night, just hours after Holcomb announced the mask order taking effect Monday to help slow the coronavirus spread. The opinion does not block the governor's action. Hill is on his way out of office after failing to win the Republican nomination for reelection following allegations that he drunkenly groped four women.
The Republican leader of the state Senate praised Holcomb's decision to drop the possible misdemeanor offense.
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The state has extended its current capacity limits for restaurants and bars and other restrictions for at least another two weeks because of an increasing number of coronavirus cases across the state. Holcomb first delayed lifting those limits two weeks ago, but he said Wednesday that a continuing volatile environment in Indiana and other states prompted him to keep them in place for at least two more weeks. Holcomb's decision means Indiana restaurants will continue to be allowed 75% capacity in their dining rooms, while bars, nightclubs, bowling alleys, museums and movie theaters can be open at half capacity.
The Associated Press contributed to this report.