Texas Governor Greg Abbott has ordered face coverings to be worn in public as coronavirus cases rocket in the state.
The directive applies to counties with 20 or more Covid-19 cases, which covers most of Texas' 254 counties.
Texas hit a record of more than 8,000 virus cases in a day on Wednesday, up from about 2,400 two weeks ago.
Americans are about to mark the Fourth of July weekend, with some beaches coast to coast shut and fireworks displays cancelled.
There have now been 2.7 million recorded infections nationwide and more than 128,000 deaths since the pandemic began.
What did the Texas governor say?
"Wearing a face covering will help us to keep Texas open for business," Mr Abbott said, announcing the order.
After an initial warning, those who refuse will face a fine up to $250.
"Let me be clear: no-one can ever be put in jail for violating this safe practice," the governor said.
"Covid-19 is not going away," Mr Abbott, a Republican, said on Thursday. "In fact it's getting worse."
Warning that some hospital intensive care units were almost full, he added: "We are now at a point where the virus is spreading so fast there is little margin for error."
The order includes a series of "common sense" exemptions, including children who are 10 years old or younger, those who have a medical condition that prevents them from wearing a mask, people who are eating or drinking and those who are exercising outdoors.
Texas is now one of 21 states that require mask wearing in public, according to Masks4All, a volunteer advocacy group.
But the move by Mr Abbott was described as "far too little, far too late" by the Texas Democratic Party.