When Natalia Kossman walked into EVR nightclub around 10 on a Friday night last month for a friend’s 30th birthday bash, she was expecting a bouncer — but not one who shills for a charity.

“That will be $20, please,” says James Lukban, 24, guarding a lockbox stuffed with $20 bills and a string of orange admission bracelets.

Lukban was hired to collect cash at the door for the Lollipop Theater Network, which screens current movies to hospitalized children.

Kossman, 30, forked over $80 total for four friends before going inside for film producer Jonathan Shukat’s birthday party-cum-fund-raiser.

“I know it helps kids,” she says, with a shrug.

Her Russian friend Olya Volk is bewildered. “We don’t pay for birthday parties in Russia,” she says.

With a free open vodka bar for a portion of the night courtesy of EVR, and friend DJ Phresh spinning pro bono, Shukat still netted $1,500 for Lolliop — after spending a few hundred dollars for out-of-pocket incidentals from the evening’s proceeds.

Inside, Shukat addresses his friends and supporters from a podium. He thanks the crowd for their support — but not before reminding them about the raffle: “It’s only $2 a ticket, guys, for all this swag!” he says.

“Keep it up and give a lot of money,” adds his mom Evelyn from the DJ booth.

“Tonight is Jonathan’s 30th birthday!”

Forget party hats and a glass of champagne — more altruistic New Yorkers are insisting on throwing birthday bashes with mandatory charity donations.

Last month at his 39th birthday bash, actor Leonardo DiCaprio raised a cool $3 million for his namesake charity, the Leonardo DiCaprio Foundation, which supports environmental causes, including saving the sharks. In October, “Wolverine” star Hugh Jackman netted $1.85 million for the Motion Picture & Television Fund for his 45th birthday at Hollywood’s Dolby Theatre. And designer Rachel Roy cashed in on the birthday charity bandwagon, raising north of $20,000 for Charity Water for her 39th birthday earlier this year.

But the trend isn’t limited to celebrities, socialites and their deep-pocketed friends. Workaday New Yorkers are now expected to shell out to celebrate — or risk being branded a Scrooge.

Last year, Kossman’s boyfriend Daniel Green held his 34th birthday party at Bryant Park Hotel, also raising money for Lollipop.

Were there any complaints?

“There will always be cheapskates,” concedes Green, who notes that some of his guests balked at shelling out $20 bucks to attend his birthday fund-raiser.

“If they don’t cough up the money, it’s more about them. When you’re talking about terminally ill children, it says more about your character.”

Not so, insist some put-upon party guests.

“I’ve probably been invited to five birthday party fund-raisers in the last six months,” says Josh, a 30-year-old entrepreneur from Murray Hill, who asked that his last name not be used for fear of looking stingy.

“One was for cancer because his grandpa died of cancer. You can’t say no to that! It was $75. It’s the obligation: ‘You’re not my friend unless you do this.’ ”

When a longtime friend held her philanthropic fête this summer to save the puppies — with a hundred dollar mandatory donation — he griped, but still gave: “The societal pressure forces you to get on board because it’s considered a good cause. It would be such a faux pas to say no to it — you don’t want to be the one guy who doesn’t save the puppies. I know everyone thinks it, but no one wants to be perceived as cheap.”

Etiquette experts say the arrangement, however well-intentioned, can be fraught with peril.

“I don’t think you should hitch your birthday to your charitable cause,” says author Henry Alford. “It seems a little crass to me, regardless of that charitable aspect. Your birthday and your cause should be honored separately: What if your friends don’t share your interest in anti-fracking measures or transgendered rights? Do you really want to test your friendship’s parameters like that?

Adds Daniel Post Senning, great-great-grandson of Emily Post and spokesperson at the Emily Post Institute: “You have to be understanding of people who don’t want to come and be accepting if they don’t want to spend the money or back a particular charity. As a guest, you don’t have to feel bad about not attending — if you can’t afford it, it’s a reasonable decision to make.”

But despite the potential for awkwardness, the trend is growing.

“Everyone now has that party-for-a-purpose mentality. Third-party fund-raising is huge,” says Carli Roth, co-founder of Host Committee, who just celebrated her own 28th birthday bash by raising $2,500 for the Building Blocks charity last weekend in the Meatpacking District.

Roth estimates that 25 percent of Host Committee’s business — a 2012 startup that acts as a third-party fund-raiser and party-planning service — are charity birthdays. The first $20 of each ticket goes back to Host Committee for the cost of the event, with a guaranteed open bar for the first hour of the party.

“People can raise between $2,000 and $5,000 at their birthday party — it’s a big feeling of achievement,” says Roth.

And while some put no limits on the amount they’ll try to raise for a favorite charity, other hosts try to keep people’s bank accounts in mind.

“I’m sensitive to people’s financial situation — that’s why we had a $20 flash sale that I sent out to all my girlfriends,” says real estate sales executive Katie Thiele of her 30th birthday blowout, which raised money for prostate cancer. “All I’m asking is for people to donate to my charity — this is all the present this 30-year-old needs.”

Mandatory tickets to her birthday bash last month at 55 Gansevoort cost $45 at the door.

So do friends mind paying to party with the birthday girl?

“They’re in the giving mindset,” she insists.

“It’s just a part of living in New York — to spend a little money to gain the best experiences out there. New York is such a monster — it loves fund-raisers and parties, and this is my way of doing what I can to raise awareness.”

But it was Alana Tendler who really cleaned up this year for her 26th birthday last month at a Highline Ballroom bash, replete with a Billy Joel tribute band and kosher Korean barbecue.

“I raised $5,000 for my birthday,” says Tendler, who is supporting JICNY, which fosters Jewish identity among young internationals. She recently became the organization’s executive director.

Her e-mail to 100 friends was simple, but direct: “I said, ‘I have every single thing I need — I don’t want dinners or presents. All I want is for you to support JICNY, which is to support me.’ ”

Even with the steep $150 ticket price for JICNY’s annual gala, Tendler’s friends who couldn’t attend came through with donations for as little as $10.

“I didn’t expect everyone to come — it’s expensive and that’s not how everyone wants to spend their time and money. I had a certain goal — and we doubled that.”

But even the broke friends can still win brownie points: “One friend was having a financial struggle, and she said, ‘I love you and support you in every way. I’m in no position to donate to the cause right now.’ But she was so supportive in terms of emotional support,” says Tendler.

Too bad emotional support doesn’t get you past the velvet rope.