Ann M. Starrs is president and CEO of the Guttmacher Institute. The views expressed in this commentary are solely those of the author.

(CNN) Social conservatives opposed to women's health, rights and autonomy now control the White House, both houses of Congress and, at the state level, most governors' houses and legislatures. Even as these policymakers continue their assault on abortion rights, they are also poised to enact policy that will undercut US women's access to family planning services.

The groundwork for this onslaught against high-quality, affordable contraceptive care is being laid in Congress and the Trump administration. It will be broad-based and has the potential to leave many US women worse off than they are today, according to research published by the Guttmacher Institute. Full or partial repeal of the Affordable Care Act in particular would leave millions of women entirely without health insurance, while tens of millions more would see their insurance's contraceptive coverage severely degraded . Care for millions more is at risk from attacks on publicly funded family planning programs and providers, particularly Planned Parenthood, that are critical for low-income women, women of color and the uninsured

It's the details that really matter here. The proportion of women of reproductive age (15-44) who were uninsured has dropped by more than a third over the first two full years of ACA implementation, driven both by states' expansions of Medicaid eligibility and gains in affordable private insurance. As efforts by congressional Republicans to repeal or otherwise scale back the ACA continue, it is unclear to what extent these gains in insurance coverage will be preserved. But the ACA has not only helped millions finally afford health insurance, it has also enhanced the quality of coverage for many others, including those who obtain insurance through their employers.

Yet one of the ACA's most critical such advances for women, the contraceptive coverage guarantee, may soon be gutted. The guarantee requires most private insurance plans to cover 18 distinct contraceptive methods without out-of-pocket costs, such as copays or deductibles.

This helps ensure women can choose the contraceptive method that works best for them, including IUDs and implants that often have high upfront costs. Some 55 million US women are currently covered by the ACA's birth control benefit and for them, the policy has led to a steep decline in out-of-pocket costs for IUDs, the pill and other popular methods, saving women and families $1.4 billion in 2013 alone . But Tom Price, the new secretary of the Department of Health and Human Services , has been openly hostile to this policy and the Trump administration could revoke or undermine it at any time.

Members of Congress and others often argue that making birth control pills available over the counter could replace the ACA's birth control benefit. While moving the pill to over-the-counter status has merit if it complements other efforts to make birth control accessible, it is utterly inadequate if done as a substitute for them. It fails to give women the choice of a broad range of birth control methods, and would increase costs for women who currently get their birth control without out-of-pocket costs. Plus, it will likely be years before any version of the pill makes it through the regulatory process necessary to become available over the counter.

Once the White House and conservative members of Congress have their way, women who lose insurance coverage, or who once again face steep out-of-pocket costs for birth control, may well turn to the nation's network of publicly supported family planning providers for low- or no-cost care. But this essential safety net is already strained to the breaking point, even without an influx of new clients.

The need for publicly funded contraceptive care increased by 5% between 2010 and 2014 , rising most among those with the lowest incomes, and among Hispanic and black women. One in four women who need publicly funded care is uninsured. But social conservatives have their sights set on this invaluable source of care, too, vowing to go after programs critical to its existence, such as Title X, as well as many of its most effective providers.

In particular, leading anti-choice groups, like the Susan B. Anthony List and Americans United for Life, along with their allies in Congress, the administration and various state governments, are determined to exclude Planned Parenthood, a vital source of care for many women, from federal funding. These proponents of "defunding" Planned Parenthood argue that other providers, namely health departments and federally qualified health centers, could step up to fill the gap.

Not so. Planned Parenthood health centers consistently perform better than other types of publicly funded family planning providers across a range of key indicators: They are much more likely to offer a full range of birth control methods and same-day insertion of IUDs or implants, and to fill prescriptions for the pill on site. They are also much more likely to routinely handle large caseloads of contraceptive clients, to get women in for appointments in a timely manner, and to offer evening and weekend appointments. And in some communities, Planned Parenthood is the sole source of publicly funded contraceptive care.

In short, it is simply not feasible for other safety net providers that are often already stretched thin to quickly step up and provide timely, high-quality contraceptive care to the many women who might suddenly be unable to obtain care if their local Planned Parenthood has been shut down. And keep in mind that none of this would happen in isolation: Health departments and federally qualified health centers may have to cope not just with the influx of former Planned Parenthood patients, but also those who could lose the insurance they gained under the ACA or who have had their contraceptive coverage gutted.

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The threat to affordable, high-quality health coverage and care, particularly when it comes to contraception, is real and urgent. And it is women — foremost women of color, women who are uninsured, low-income, young or otherwise disadvantaged — who will pay the price.