Stagehands at theatres on Broadway in New York have gone on strike, shutting down more than 20 plays and musicals including The Lion King and Mamma Mia.
Broadway is considered one of New York's main tourist attractions
The stagehands, who work with lighting, sound, scenery and special effects, are picketing outside theatres.
The strike comes after three months of negotiations between producers and a union about pay and working conditions failed to produce an agreement.
No new talks are scheduled and it is unclear how long the strike will last.
All but eight Broadway shows have been shut down and producers say they plan to pay refunds to people who have bought tickets for cancelled shows.
A long strike could spell disaster for shows that have actors on short contracts or little in the way of advance sales.
It comes at a time that is traditionally one of Broadway's busiest of the year.
The lights last went out during a strike by musicians four years ago.
Lasting four days, that strike cost the city about $7m (£3.3m) a day, city tourism officials said at the time.
This is the first time the Local One stagehands' union has called a strike on Broadway.
New York mayor Michael Bloomberg said he had spoken to both the theatre owners and the stagehands.
"While this is a private labour matter, the economic impact is very public and will be felt far beyond the theatres closed today," he said, adding that "the city continues to stand ready to help in any way we can."
The dispute has largely been over work rules that govern how many stagehands must be called for work, how long they work, and what kind of tasks they can perform.
The League of American Theatres and Producers wants more flexibility in those rules so as to avoid paying for workers who have nothing to do.
"Our goal is simple - to pay for workers we need and for work that is actually performed," Charlotte St Martin, executive director of the league said.
But the union says theatre owners have been unclear about what offsetting benefits stagehands can have in return.
Actor Patrick Page, star of How The Grinch Stole Christmas, said he supported the strike but hoped for an early settlement:
"These guys on strike over here are the backbone of Broadway. They are the guys who keep me safe, when I get hoisted up in the air in the show, they are the guys who put light on me, who make sure everything happens."
"I know that the Actors Equity Association really supports the guys at Local One, I am a member of the union and we all just want the shows to happen again," he said.
The Broadway strike follows hot on the heels of a separate screenwriters' strike which began in Hollywood last week, prompted by a disagreement over royalty payments.