WASHINGTON — Senate Republicans say they’re open to extending a pot of Affordable Care Act funds that will expire at the end of the year — but only if Democrats acquiesce to stricter abortion restrictions on insurance plans.

The demand presents a significant hurdle to reaching a bipartisan deal to extend ACA funding designed to avoid major premium hikes next year for more than 20 million Americans, as Democrats are adamant that existing abortion guardrails under Obamacare are sufficient.

If the funds are not extended by the end of the year, some people insured under Obamacare could see their bills rise by thousands of dollars per month, raising concerns that millions will choose to go uninsured.

Senate Majority Leader John Thune, R-S.D., said there will be a negotiation about an extension after the government reopens. He said one condition will be stricter rules pertaining to the Hyde amendment, which bars federal funding from being used for abortion.