Lauren Ambrose, the Tony-nominated star of Lincoln Center Theater’s hit revival of “My Fair Lady,” finds the role of Eliza Doolittle too taxing to perform eight times a week.

So she’s skipping Sunday matinees and having her understudy go on.

That doesn’t sit well with her co-star, the great Dame Diana Rigg, who plays Henry Higgins’ formidable mother.

Rigg is annoyed that nobody from Lincoln Center told her or the rest of the cast that Ambrose decided to reduce her workload.

“I learnt, courtesy of a newspaper, that our leading lady will not be appearing in future Sunday matinees,” Rigg wrote in an email obtained by The Post. “Now call me old-fashioned, which I unashamedly am, but I don’t think this development is fair to audiences. They have booked their seats in advance, paying an exorbitant price for them to see what they have been led to believe is the original cast. The very least we can do as actors is to acknowledge their presence as a privilege and take care never to abuse it.”

She concluded: “It is time managements put their audiences first and insist on the old adage, slightly adapted by me, ‘The show must go on — with ALL principals.’”

I called Rigg, who was also up for a Tony for her role in the show, and she said she thinks the world of Ambrose — “she is giving a definitive performance” — but is struggling to accept the work ethic of younger performers.

“I’m flying the old flag for a generation of actors who performed even when they were at death’s door,” the 79-year-old says. “But I suppose it’s a tradition that has been lost. It’s the norm these days, so I guess I should just shut up.”

‘I’m flying the old flag for a generation of actors who performed even when they were at death’s door.’

In a statement released by Lincoln Center Theater, artistic director André Bishop says, “The decision for Lauren to perform seven performances a week was made due to the intense demands of this enormous, taxing role. Eliza requires a singing actress who can belt and sing in a high, operatic range as well. Julie Andrews often said and wrote that there were performances of ‘My Fair Lady’ when she wasn’t sure she could make it to the end of the show. The most important thing is that Lauren protect her stamina to continue to deliver beautiful shows to our audiences.”

Production sources say Ambrose, best known for TV’s “Six Feet Under,” isn’t used to the grueling demands of an eight-show week, although she’s performed two nonsinging roles on Broadway. They say she’s also been fretting about not spending enough time with her husband and their two children.

“She lives up in the country somewhere, in a kind of crunchy-granola place, and she’s worn out by the show,” a production source says. “Diana is right that we were all surprised. [Ambrose] came in the other day and just told everybody she’s dropping the Sunday matinee. I think André or Bart [Sher, the director] might have said something to us.”

Rigg says Ambrose’s decision to spend more time with her family is “perfectly understandable,” adding that her understudy, Kerstin Anderson, is “spectacularly good.”

But Rigg believes it’s an actor’s job to show up. She won a Tony Award in 1994 for her star turn in “Medea,” even though she busted a vocal cord in rehearsals.

“They put a camera down my throat, and I could see the tear,” she says. “There was a note in the spectrum of my voice that I could not hit. No sound would come out. So I had to re-orchestrate all those speeches and arias to avoid that note. It was a fascinating exercise in learning how to keep going.”

Did she ever think of taking a few days off?

“Never.”

You can hear Michael Riedel every weekday morning on “Len Berman and Michael Riedel in the Morning” on 710 WOR radio.