(CNN) In a blow to Obamacare's controversial contraceptive mandate, employers may now have more leeway to withhold birth control coverage on religious grounds, according to new rules issued by the US Department of Health and Human Services on Friday.

The new rules continue the undermining of the Obamacare mandate that requires birth control be covered with no co-pay as a preventive service. This could impact many of the millions of women who now receive contraceptives at no cost under this provision.

The rules would let a broad range of employers -- including nonprofits, private firms and publicly traded companies -- stop offering contraceptives through their health insurance plans if they have a "sincerely held religious or moral objection," senior agency officials said on a call about the implementation and enforcement of the new rules.

Health and Human Services officials said the new rule would have no impact on "99.9% of women" in the United States. It is basing that percentage on the 165 million women in America, many of whom are not in their child-bearing years.

The agency calculated that at most, 120,000 women would be affected: mainly those who work at the roughly 200 entities that have been involved in 50 or so lawsuits over birth control coverage.

Policy experts, however, argue that this could open the door to hundreds of employers dropping coverage. For instance, there are hundreds of Catholic hospitals, nursing homes and nonprofits that may want to stop providing contraceptives, said Tim Jost, emeritus professor at the Washington and Lee University School of Law.

Friday's action consists of two rules, according to a Health and Human Services statement: First, entitles that have "sincerely held religious beliefs" against providing contraceptives would no longer be required to do so. The second rule extends the same provision to organizations and small businesses that have objections "on the basis of moral conviction which is not based in any particular religious belief."

The latest announcement builds upon an executive order in May claiming "to protect and vigorously promote religious liberty" by providing "regulatory relief" for organizations that object on religious grounds to Obamacare coverage requirements for certain health services, including contraception.

"We will never, ever stand for religious discrimination. Never, ever," President Donald Trump said at the time.

A number of legal challenges to the new rules are brewing from groups such as the American Civil Liberties Union, the National Women's Law Center, the Center for Reproductive Rights and the office of California Attorney General Xavier Becerra.

The ACLU filed a lawsuit Friday. The organization's senior staff attorney Brigitte Amiri called the administration's rules "blatantly unconstitutional."

Until now, a fairly limited number of employers -- mainly churches and some other religious entities -- could get an exemption to the mandate. Some others, such as religious-based universities or hospitals, could seek accommodations so that they didn't have to provide coverage, but their workers could still get covered contraceptives that would be paid for by the insurer or the employer plan's administrator.

Over 55 million US women have birth control coverage with zero out-of-pocket costs, according to the National Women's Law Center. The mandate saved women an estimated $1.4 billion on birth control pills alone in 2013, according to the center.

Experts have pointed out that many women use birth control methods for more than pregnancy prevention, including treatment of hormonal imbalances and endometriosis.

"There is no way to know how many women will be affected," said Alina Salganicoff, director of women's health policy at the Kaiser Family Foundation, a nonprofit that focuses on health policy research and communications.

"HHS leaders under the current administration are focused on turning back the clock on women's health," Dr. Haywood L. Brown, president of the American Congress of Obstetricians and Gynecologists, said in a statement. "Reducing access to contraceptive coverage threatens to reverse the tremendous progress our nation has made in recent years in lowering the unintended pregnancy rate."

Brown said that weakening contraception coverage could also take a toll on maternal mortality, community health and economic stability of women and families.

"Birth control is not controversial -- it's health care the vast majority of women will use in the course of their lifetime," Cecile Richards, president of Planned Parenthood Federation of America, said in a statement.

"Nine out of ten women of reproductive age will use birth control in their lifetime. This administration is carrying out a full-scale attack on birth control," Richards said. "We cannot allow President Trump to roll back the progress women have made over the past century."

Friday's move comes more than three years after the US Supreme Court ruled that "closely held corporations" -- in that case, Hobby Lobby -- could be exempt from providing certain kinds of birth control to their employees.

Attorney General Jeff Sessions also released "interpretative guidance" Friday directing all federal agencies to comply with existing protections for religious liberty under federal law and Supreme Court precedent.

"The constitutional protection of religious beliefs and the right to exercise those beliefs have served this country well, have made us one of the most tolerant countries in the world, and have also helped make us the freeist and most generous," Sessions said in a statement. "President Trump promised that this administration would 'lead by example on religious liberty,' and he is delivering on that promise."

A Justice Department official explained, however, that Sessions' directive is limited in scope: "It's not a policy document. It doesn't create or authorize the creation of any new protections. It simply summarizes the state of the law as it exists today."

The official explained that the department's guidance was issued because Trump directed Sessions to do so in his May executive order.

When asked what was different between Thursday and today, the official said, "nothing, as a matter of law."