UPDATE: 5:45 p.m. -- Heritage Action says it opposes House Republicans' latest government funding proposal, arguing that seeking a delay of the individual mandate in the new health care law "would do little to stop Obamacare's massive new entitlements from taking root."

Republican House leaders proposed Monday a short-term continuing resolution that would delay for a year an Obamacare provision that requires nearly everyone buy health insurance or pay a fine. The proposal would also eliminate an employer contribution subsidy that now helps pay for insurance for Congress and its staff.

"Much like the rest of Obamacare, the individual mandate and staffer exemption are bad policy, but the proposed changes would not keep the law from taking root," Heritage Action said in a statement. "For that reason, Heritage Action opposes the amendment, but will not key vote against them." The conservative group Heritage Action insists that the repeal of the medical device tax proposed by Republicans is insufficient to garner its support on a continuing resolution that would keep the government open.

Heritage Action is among the conservative advocacy groups that have been pressuring Republican lawmakers to defund Obamacare before implementation began in earnest on Tuesday.

ORIGINAL STORY: Heritage Action spokesman Dan Holler said that a temporary spending bill that would keep the government open past midnight Monday and repeal a medical device tax included in Obamacare "falls woefully short of what is necessary to protect Americans from Obamacare."

House Republicans have tried to defund Obamacare and then to delay it for a year, but both proposals were rejected by the Democratic Senate. With the shutdown now looming, GOP leaders are looking for an alternative that would appease party conservatives and force the Senate to accept some changes in the new health care law. The medical tax device is seen by many as a change Democrats may be willing to consider.

But Heritage Action, a leading outside voice in the push to defund Obamacare, quickly criticized the repeal of the tax.

The Republican proposal "does nothing to prevent the law’s entitlements from taking root and continues funding Obamacare in its entirety," Heritage Action said.

The statement also pointed to the possibility that "Sen. Harry Reid will ... return the CR with nothing but the Medical Device Tax repeal" and made it clear that the organization would "strongly oppose" such legislation.

However, a separate piece of legislation passed by the House would fund the U.S. military, which Heritage Action supports.

"Seems like that could clear the Senate by [unanimous consent] and head straight to the president without any intervening drama," Holler said.