There’s a new fairy-tale front in the “War on Women”: a paid family- and medical-leave entitlement.

It’s supposed to be the magic cure-all for expectant mothers and workers with sick loved ones suffering in evil corporate America.

In fact, it’s another “one size fits all” mandate that would hurt more folks than it helps — and means particular trouble for women in the workforce.

In the wake of ObamaCare’s graveyard of broken promises — from the “if you like your plan, you can keep it” whopper to the way the laughably named “Affordable Care Act” hiked most Americans’ insurance costs — people may be more skeptical about the Democrats’ latest plan.

The leading paid-leave proposal comes from Sen. Kirsten Gillibrand (D-NY). Her Family and Medical Insurance Leave Act would upend the current compensation packages of 146 million American workers to create a massive, new, federal paid-leave entitlement.

It hits all workers with a new payroll tax so they can be eligible for paid time off at a set percentage of normal salary.

A guaranteed benefit sounds nice, but many will find they are worse off than before, with less take-home pay and less generous overall leave time.

Mandating a single system will also discourage companies from considering work-from-home and part-time arrangements, which are often the best solution for both worker and employer when people need leave.

Women should especially be warned: Proposals like the Family Act create the expectation that women will disappear for three months at a time, making them seem less suitable for leadership positions.

Liberal champions of generous leave programs ignore it, but that’s exactly what’s happened in Europe, where paid-leave mandates have left women much less likely than Americans to be managers and private-sector executives.

Gillibrand’s bill is the opposite of helping women “lean in.”

Let’s also consider the facts now about the state of leave benefits in US workplaces. Liberals paint a bleak picture of a hypersexist “Mad Men” world, but that simply isn’t reality: Most companies already recognize that commonsense leave policies are important for holding on to valued employees.

For example, the Census Bureau has studied what actually happens to working women after the birth of a child: 56 percent of full-time working women used paid leave, 42 percent used unpaid leave, 10 percent used disability leave, 19 percent quit their job and nearly 5 percent reported being let go.

(The percentages add up to more than 100 because many women used more than one category of leave.)

The Census data don’t suggest that all Americans have adequate benefits — for example, part-time workers were more likely to quit and had fewer leave options.

But these facts should caution against a one-size-fits-all government leave program that would disrupt all existing arrangements.

And if we decide the government should do something, far better it offer direct relief targetted at the biggest hardships created by a lack of paid leave.

A program modeled on the Earned Income Tax Credit, for example, could provide financial help for low-income workers following the birth of a child or who face significant illnesses that require extended leave time.

This could help people facing tough times without changing economic incentives for hiring them and without discouraging a flexible, dynamic work world.

Of course, the best way to ensure people have the compensation packages they need is a growing economy with plentiful jobs, so that employers have to compete for workers.

Sadly, that seems a distant dream today. But we’d only make it even more distant if we fall for the fantasy that Washington can sweep in and shower workers with generous benefits without real costs for workers.

We’ve heard that story before; it doesn’t have a happy ending.

Carrie Lukas, the managing director of the Independent Women’s Forum, is expecting her fifth child in nine years this fall. During this time, she has worked continuously for IWF using flexible, at-home arrangements.