One unusually warm evening in the West Village, while other New Yorkers were outside walking their dogs in sneakers and T-shirts, a family of five sat primly in the front window of a formal dining room, each of them garbed in a stylish blazer. A couple in a velvet corner booth wore suits — his navy, hers powder blue. Pearls gleamed, freshly buffed shoes glowed. When a fashionably dressed couple stopped in momentarily for a peek at the menu, the sight was jarring: They were wearing jeans.

That everyone was in full feather at this restaurant, Les Trois Chevaux, was no coincidence. They had been instructed to do so the previous day in a text message that read like a manifesto.

“At Les Trois Chevaux, we revere the style and finesse that can only be attributed to having New York swagger,” it said. “We expect our guests to arrive in proper dinner attire, and for you to celebrate the style that downtown New York City can bring.”

Lest there be any confusion, details followed: “Blue jeans, shorts and sneakers are strictly prohibited.” Diners were “kindly” requested to wear jackets. For those without a jacket, a vintage Yves Saint Laurent model would be provided. Anything else? “Absolutely no flip-flops,” the chef and owner, Angie Mar, emphasized in an interview.

“Something that I feel tremendously is missing from New York over the past five or six years is that old-school flair that I love,” she said. “It is important that we bring that back.”

During a pandemic in which many Americans have traded their tailored slacks for leisure wear, dress codes are making an unexpected return to the dining room.

Over the last two years, several new restaurants around the country have opened with policies on expected attire, some stern (“upscale fashionable dress code strongly enforced,” warns a text from Olivetta in Los Angeles) and some vague (“smart casual or better,” advises Catbird in Dallas).

Some are aspirational: “We expect our guests to bring their best,” says Kitchen + Kocktails in Chicago. Others seem to allude to some disturbing prior incident: “Clothing emitting offensive odors is not permitted” at Juliet in Houston.

Whatever the particulars, the calculation is the same — a belief that many diners are eager to dress up again after an epoch of record-level dowdiness.

“Everywhere we went, people were walking around in sweatpants and T-shirts and their hair was not done,” said Rosea Grady, the general manager at Thirteen, a high-end Houston restaurant founded by the professional basketball player James Harden that opened in March 2021. “We wanted Thirteen to be a place where people put their best on.”