Although most indoor live performances have been banned in New York since the coronavirus began its deadly spread in March, about a dozen people turned up Wednesday night at Birdland, the jazz club near Times Square, for a 7 p.m. performance that was billed as dinner with live jazz. They had reservations.

Among them was Tricia Tait, 63, of Manhattan, who came for the band, led by the tuba player David Ostwald, which plays the music of Louis Armstrong. Until the pandemic hit, it had performed on most Wednesdays at Birdland. She admitted to health worries “in the back of my mind,” but said, “Sometimes you just have to take a chance and enjoy things.”

Birdland, and a number of other noted jazz clubs and piano bars across the city, were quietly offering live performances again, arguing that the performers were playing “incidental” music for diners, and that the music was therefore permitted by the pandemic-era guidelines set by the State Liquor Authority. But the shows will not last long: Gov. Andrew M. Cuomo said Friday that he would close all indoor dining in New York City beginning Monday, citing troubling signs of the virus’s spread.

“We’re going to close,” Ryan Paternite, the director of programming and media at Birdland, said after the announcement. “We’re not going to flout the law.”

That the performances had been taking place at all was perhaps surprising, given that the number of daily new coronavirus cases in New York City has been climbing to levels not seen since April, in-person learning has been suspended at public middle schools and high schools, and most other indoor shows were banned.

But the clubs argued that they were following guidelines from the liquor authority, which state that “only incidental music is permissible at this time” and that “advertised and/or ticketed shows are not permissible.” The guidelines continue: “Music should be incidental to the dining experience and not the draw itself.”

That was enough for a number of New York venues that are better known for their performances than their cuisine — including Birdland, the Blue Note and Marie’s Crisis Cafe, a West Village piano bar that reopened Monday with a show tune singalong after declaring itself a dining establishment — to begin offering live music again.

“We think it’s incidental,” Mr. Paternite said of its calendar of performances that included a brass band and a jazz quartet. “It’s background music. That’s the rule.”

The state rules have been challenged in court. After Michael Hund, a Buffalo guitarist, filed a lawsuit in August challenging them, a judge in the U.S. District Court in the Western District of New York issued a preliminary injunction last month preventing the state from enforcing its ban on advertised and ticketed shows. “The incidental-music rule prohibits one kind of live music and permits another,” the judge, John L. Sinatra Jr., wrote in his Nov. 13 decision. “This distinction is arbitrary.”

The state is appealing the ruling.

“The science is clear that mass gatherings can easily turn into superspreader events, and it is unconscionable that businesses would attempt to undermine proven public health rules like this as infections, hospitalizations and deaths continue to rise,” William Crowley, a spokesman for the liquor authority, said Thursday. He noted that a federal judge in New York City had ruled in another case that the restrictions were constitutional. He said that the state would “continue to vigorously defend our ability to fight this pandemic whenever it is challenged.”

But it is far from clear what, exactly, “incidental” music means. Does that mean a guitar player in the corner? A six-person jazz band like the one that played at Birdland on Wednesday night? The Harlem Gospel Choir, which had been set to perform at the Blue Note on Christmas Day? Mr. Crowley did not respond to questions seeking further clarity on Thursday, or about what enforcement actions the state has taken.

Robert Bookman, a lawyer who represents a number of New York’s live music venues, said venues interpreted the ruling as allowing them to advertise and sell tickets for incidental music performances during dinner.

So venues had been choosing their words carefully. They were taking dinner reservations, and are announcing calendars of lineups for what Mr. Paternite, of Birdland, characterizes as “background music during dinner.” Unlike Mac’s Public House, the Staten Island bar that declared itself an autonomous zone and was recently lampooned on “Saturday Night Live,” they have no interest in openly flouting regulations.

Mr. Paternite said that Birdland, after laying off nearly all of its 60 employees in March, came back with what he called a “skeleton staff” of about 10 people.

“It’s a huge risk for us to be open,” he said. “And it only brings in a pittance. But it helps us out in our agreement with our landlord, because to pay our rent over time and stay current on our utilities and taxes, we need to stay open. But we’re losing massive amounts every day.”

Mr. Cuomo, in announcing the pending closure of indoor dining, called for federal aid to help bars and restaurants survive, and for a moratorium on commercial evictions.

If venues are unable to reopen now, Mr. Paternite fears, they may never do so. The Jazz Standard, a beloved 130-seat club on East 27th Street in Manhattan, announced last week that it would close permanently because of the pandemic. Arlene’s Grocery, a Lower East Side club that hosted the Strokes before they became well known, said it was “on life support” and, without aid, would have to close on Feb. 1.

Randy Taylor, the bartender and manager at Marie’s Crisis Cafe, said the last time the piano bar had served food was probably back in the 1970s — or perhaps earlier. “There’s a very old kitchen that’s totally disconnected upstairs,” he said. Its dining options had been extremely limited: It was offering $4 bowls of chips and salsa. “We are required to sell them,” he said. “We can’t just give them away.”

Shortly before the indoor dining ban was announced, Steven Bensusan, the president of Blue Note Entertainment Group, said that he hoped it could be avoided.

“I know cases are spiking,” he said. “But we’re doing our best to keep people safe, and I hope we can continue to stay open. We’re not going to be profitable, but we have the ability to give some people work who’ve been with us for a long time.”

The clubs said they had been taking precautions. At the Blue Note, which reopened Nov. 27, the formerly shared tables were six feet apart and separated by plexiglass barriers, and its two nightly dinner seatings were each capped at 25 percent capacity, or about 50 people. At Marie’s Crisis Cafe, where the masked pianist Alexander Barylski was ensconced behind clear shielding on Wednesday night as he led a jubilant group chorus of “Frosty the Snowman,” Mr. Taylor said that tables were separated by plastic barriers, and that the venue conducted temperature checks and collected contact tracing information at the door.

Marie’s Crisis Cafe had been livestreaming shows on Instagram and its Facebook group page, but Mr. Taylor said it wasn’t the same. On Wednesday night, 10 customers belted out holiday tunes through masks, some sipping their first drinks at a venue since March.

“There have been some tears,” Mr. Taylor said. “People really, really missed us. We can’t see their smiles through their masks, but their eyes say it all.”

He said that he heard the news that indoor dining would be banned again while he was at Sam’s Club buying more chips and salsa for the bar.

“We’re closing and locking everything down, but we’ll be ready to go whenever we can go again,” he said. “It makes me sad because I had such a great night last night.”