It’s not just individuals without employer health coverage who could lose big under the newly revised version of the Republicans’ American Health Care Act.

People who get health coverage from their jobs could be left swinging in the wind, too—in fact, as many as half of all such employees could be affected.

That’s according to an Alternet report that says an amendment added to the bill currently being considered by the House of Representatives would allow insurers in states that get waivers from regulations put in place by the Affordable Care Act to deny coverage for 10 types of health services—including maternity care, prescription drugs, mental health treatment and hospitalization.

An MSNBC report points out that “because the Republican-led House is scrambling to pass a bill without scrutiny or serious consideration,” the last-minute amendment’s full effects aren’t even known, since “[t]his is precisely the sort of detail that would’ve come to light much sooner if Republicans were following the American legislative process. In fact, this may not even be the intended goal of the GOP policy.”

While the ACA prohibits employer-based plans from imposing annual limits on coverage and bare lifetime caps on 10 essential benefits, the Obama administration did loosen those restrictions back in 2011, saying that employers could instead choose to follow another state’s required benefits.

What the new Republican take on the AHCA does is push that further—a lot further—by allowing large employers to pick the benefit requirements for any state. That would let them limit coverage on such costly types of care as mental health and substance abuse services.

In a Wall Street Journal report, Andy Slavitt, former acting administrator of the Centers for Medicare and Medicaid Services under President Barack Obama, is quoted saying, “It’s huge. They’re creating a backdoor way to gut employer plans, too.”

The changes to employer-based plans would hit anyone not insured by Medicare or by small-business plans, because the bill includes cuts to Medicaid and changes to the individual market as well.

A report from the Brookings Institution points out that “One of the core functions of health insurance is to protect people against financial ruin and ensure that they get the care they need if they get seriously ill.” The ACA pushed insurance plans to meet that standard, it says, by requiring them to “limit enrollees’ annual out-of-pocket spending and [bar] plans from placing annual or lifetime limits on the total amount of care they would cover.”

However, while those protections against catastrophic costs “apply to almost all private insurance plans, including the plans held by the roughly 156 million people who get their coverage through an employer,” the Brookings report says, the amendment to the Republican bill “could jeopardize those protections—not just for people with individual market plans, but also for those with employer coverage.”

How? By modifying “the ‘essential health benefit’ standards that govern what types of services must be covered by individual and small group market insurance plans. The intent of the amendment is reportedly to eliminate the federal benefit standards that currently exist and instead allow each state to define its own list of essential health benefits.”

And then, with employers allowed to pick and choose which state’s regulations they’d like to follow, a loophole the size of the Capitol building would not only allow “states will set essential health benefit standards that are considerably laxer than those that are in place under the ACA,” says the report, but “large employers may have the option to pick which state’s essential health benefits requirements they wish to abide by for the purposes of these provisions.”

The result? “[T]his would likely have the effect of virtually eliminating the catastrophic protections with respect to large employers since employers could choose to pick whichever state set the laxest standards. The same outcome would be likely to occur for all private insurance policies,” the report continues, “if insurers were permitted to sell plans across state lines, as the Administration has suggested enacting through separate legislation.”

While the actual effect of the amendment is unclear, the Brookings report concludes, “there is strong reason to believe that, in practice, the definition of essential health benefits that applied to the catastrophic protections would be far weaker under the House proposal than under current law, seriously undermining these protections. These potential adverse effects on people with employer coverage, in addition to the potentially damaging effects of such changes on the individual health insurance market, are thus an important reason that policymakers should be wary of the House proposal with respect to essential health benefits.”