Soon to be retired from the campaign trail, Mayor Bill de Blasio may ­apply one of his election-try themes at home: requiring employers to give workers two weeks’ paid vacation. This benefit sounds innocuous. Nearly nine out of 10 private-sector workers already get at least two weeks’ paid time off, according to the city’s figures — so why not make it the law?

But New York’s small businesses are struggling against high rent, competition from Amazon and onerous existing regulations; one more mandate may force employers to send staff on vacation permanently.

In January, de Blasio borrowed an idea pushed by Jumaane Williams, now the public advocate. As Williams said in May, “The United States is the only advanced economy in the world that doesn’t guarantee some level of paid leave.”

Williams’ bill would force businesses with at least five workers to offer two weeks’ paid time (less for part-time workers). Though City Council Speaker Corey Johnson has expressed pragmatic skepticism, the bill got a boost last week when Williams and Chirlane McCray, the city’s first lady, held a rally.

To see why Johnson is right to pause, talk to Natasha Amott, one of the city’s hard-pressed small-business entrepreneurs. Her goal, when she opened her first Whisk kitchen goods store in 2008, was to have a Whisk in each borough. She got to three: one in Williamsburg, one in mid-Manhattan and one in downtown Brooklyn.

Now, besieged by rising property taxes (which tenants indirectly pay) and rising rent, she was forced to close two this year, and is down to one: a homey storefront on Atlantic Avenue in downtown Brooklyn.

Amott’s risk-taking creates jobs. The remaining Whisk outlet has 10 staff, six to seven of whom work full-time — down from 23 full-timers at the company’s peak.

“Whisk jobs are meaningful jobs,” she says. And her employees take paid vacation. One full-time management employee gets 10 days; another 7½-year veteran has negotiated nearly three weeks.

But a requirement is different. Businesses already must comply with the year-old paid-sick-leave law: Some small employers tell workers they can use the five days as either sick time or vacation. “It’s a huge jump overall for businesses to triple from five to 15 days,” Amott says.

And it’s not clear the sick-leave mandate, plus a $13.50-to-$15-an-hour minimum wage, aren’t having an impact. New York’s retail businesses lost 600 jobs between 2017 and 2018, and are down 2,000 since their 2015 peak of 352,100.

The issue isn’t just financial, although Amott estimates that the vacation mandate would add as much as 4 percent to her payroll costs, or $10,000 to $14,000 — which is “absolutely meaningful to a small-business owner like me when I am faced with constantly increasing rents and real estate taxes.”

It’s also logistical: Whisk closes only two days out of the year and has to open nights and weekends.

Many high-paid office workers have flexible vacation because they have to do the same amount of work, no matter what. But in retail, “you can’t just delay the project,” Amott notes.

Vacation means other workers must cover shifts. If someone gets sick while someone is on vacation during a busy time of year, observes one employee who wished to remain anonymous, it can be a real problem: “As an employee, I’m like, yes — employee rights. But I can see [even if] we want this time off, we don’t have employees to cover” shifts.

New Yorkers who see empty storefronts may feel a certain fatalism: It must be Amazon. Amazon is a “threat,” says Gerry Geddes, who has worked for Whisk for a year and once worked for Gracious Home, a storied New York retailer whose flagship closed three years ago. But “a lot of people make a point of coming here instead of Amazon … There’s a very conscious effort.”

As Sayuri, another worker, notes, customers “really want to keep mom-and-pop stores.”

That’s not to say Public Advocate Williams doesn’t have a point: Vacation is important.

But if it’s that critical, it should be via a payroll tax on all employers, just like Social Security and Medicare.

“This is a viable business,” says Amott — but will the city keep it that way?

Nicole Gelinas is a contributing editor to the Manhattan Institute’s City Journal.