WASHINGTON (Reuters) - President Donald Trump said on Tuesday he likely will sign an order this week that is expected to allow Americans to buy stripped-down health insurance policies, a step some experts say would further undermine the Obamacare law that Trump opposes.

Unable to win passage of legislation to dismantle the 2010 law in a Congress led by his own party, Trump indicated he would take unilateral action. He offered few specifics beyond saying his action would let people cross state lines to obtain “great, competitive healthcare” costing the United States “nothing.”

The expected order would allow small businesses and individuals to band together as associations to buy health insurance plans that would be exempt from some Obamacare requirements. These include mandatory coverage for 10 essential health benefits such as maternity and newborn care, prescription drugs and mental health treatment.

It would also expand the amount of time people can use short-term medical insurance plans, which are cheaper than traditional plans but cover a limited set of benefits. People could use those plans for up to a year, compared to three months under current law.

“I’ll also be signing something, probably this week, which is going to go a long way to take care of many of the people that have been so badly hurt on healthcare,” Trump told reporters in the Oval Office.

“With Congress the way it is, I decided to take it upon myself,” Trump added, saying the plan is “largely worked out.”

White House spokeswoman Sarah Sanders said Trump will make his announcement “by the end of Friday.”

Trump said his action would let insurers sell across state lines. The association health plans, for instance, could be sold from a state with fewer benefit requirements. Such insurance policies could be cheaper than those that provide the full range of medical coverage required under Obamacare, potentially making them attractive to people in other states.

It is unclear when these plans would become available. It is unlikely consumers could sign up for these plans during the 2018 open enrollment period, which begins Nov. 1.

U.S. President Donald Trump meets with former U.S. Secretary of State Henry Kissinger in the Oval Office of the White House in Washington, U.S., October 10, 2017. REUTERS/Kevin Lamarque

Experts questioned Trump’s authority to issue such an order that would exempt some plans but not others from Obamacare rules rather than pursuing the changes through legislation. The action could open Trump to legal challenges from Democratic state attorneys general, who have said they will sue Trump if he tries to destroy Obamacare.

The plans allowed under the order could lure young and healthy people away from the individual insurance markets created by the 2010 Affordable Care Act, dubbed Obamacare. That could further destabilize those markets, where insurers have already exited the markets altogether, pared back offerings or hiked premiums because of uncertainty caused by the Trump administration.

Experts said Trump’s plan could leave behind only the sickest people in the Obamacare markets, raising premiums and effectively eroding the law’s protection that people with pre-existing medical conditions cannot be charged more.

‘HURT RATHER THAN HELP’

“There’s a general belief that at every turn the federal government is going to create regulations to hurt rather than help the markets,” said Craig Garthwaite, director of the healthcare program at Northwestern University’s Kellogg School of Management, referring to the Trump administration.

“It unwinds the ability of people with pre-existing conditions to get insurance under the ACA,” Garthwaite said.

Republicans have failed to make good on their seven-year promise to repeal and replace Obamacare, the signature domestic policy achievement of Trump’s Democratic predecessor Barack Obama. Gutting Obamacare was a top Trump campaign promise.

Trump, who has called the law a failure and vowed to let it “implode,” has undermined Obamacare through regulatory and administrative actions.

Last week, the U.S. Department of Health and Human Services issued a rule that will let businesses and non-profit organizations lodge religious or moral objections to obtain an exemption from the law’s mandate that employers provide birth control for women in health insurance with no co-payment.

Trump has declined to commit to making payments guaranteed to insurers under Obamacare. The payments are estimated to be about $7 billion this year and help lower out-of-pocket medical costs for low-income consumers. Insurers have cited that uncertainty in exiting insurance markets or hiking premiums.

His administration has slashed the Obamacare advertising budget, halved the open enrollment period and cut funding to groups that help sign people up for insurance under the law.