The Trump administration has dramatically expanded the number of employers allowed to flout the Affordable Care Act (ACA) policy that requires company healthcare plans to cover contraception at no additional cost.

Two new federal rules could result in a loss of contraception coverage for thousands of women, a reality the drafters acknowledged, writing the change “will result in some persons covered in plans of newly exempt entities not receiving coverage or payments for contraceptive services”.

Under the new rules, publicly traded for-profit companies can opt out of the so-called contraception mandate by citing a religious or a moral belief, whether or not the company has a religious purpose. Universities are also eligible to opt out of providing contraception to any students they insure.

Under Barack Obama, only religiously affiliated employers such as Christian colleges and companies with a “closely held” ownership structure were eligible to opt out of the contraception mandate based on religious beliefs.

Before the rules were even published, reproductive rights groups vowed to try to block them in court.

“Any rule that allows employers to deny contraceptive coverage to their employees is an attempt at allowing religion to be used as a license to discriminate,” said Louise Melling, deputy legal director of the American Civil Liberties Union (ACLU). “We’ll see the Trump administration in court if they try to follow through on these plans.”

On Friday, Fatima Goss Graves, president of the National Women’s Law Center, said the group would “take immediate legal steps to block these unfair and discriminatory rules”.

White House spokeswoman Sarah Huckabee Sanders said the White House was prepared to fight and win a legal battle. “It’ll show that this administration is on the right side of the law,” she said.

The president of the American Congress of Obstetricians and Gynecologists, Dr Haywood Brown, said the Trump administration was “focused on turning back the clock on women’s health”.

With the new rules, the Trump administration has substantially weakened one of the most controversial ACA policies, one that greatly expanded access to affordable contraception.

The Obama administration adopted the mandate in 2011, a year after the passage of the ACA, to comply with that law’s requirement that health insurance plans fully cover preventive health benefits for women.

The percentage of privately insured women who paid out-of-pocket for contraception subsequently dropped from 20% to 4%, according to the Kaiser Family Foundation. By one estimate, the mandate has saved US women $1.4bn on birth control.

Scores of employers objected to the mandate in court. Many were Catholic groups citing moral beliefs that prohibited artificial interference with procreation. Others cited a scientifically dubious belief that some forms of contraception cause abortions.

In 2014, arguing that federal law protected their beliefs, the owners of the craft supply giant Hobby Lobby sued the government in the supreme court. A 5-4 decision granted corporations with a “closely held” ownership structure the ability to opt out of the mandate.

Donald Trump laid the foundation for rolling back the mandate further in early May, when he signed an executive order directing his administration “to address conscience-based objections” to covering birth control. Present at the signing were several nuns from the Little Sisters of the Poor, a religious order that attempted to further weaken the mandate after the Hobby Lobby decision.

“With this executive order, we are ending the attacks on your religious liberty,” Trump said.

The new rules announced on Friday also compromise the government’s ability to cover the contraceptive needs of women whose employers cut their benefits.

Under Obama, religiously affiliated organizations seeking to opt out were required to notify the US health department. The Trump rules allow these and other employers to stop providing contraception coverage without notifying the government – although they would need to notify employees.

The reason is that many groups, the Little Sisters included, saw notifying the government as tantamount to actually providing the coverage, because the government could act on that notification to make alternate arrangements for coverage.