(CNN) -- The U.S. government shutdown went into effect at 12:01 a.m. ET Tuesday after lawmakers in the House and the Senate could not agree on a spending bill to fund the government.
The two sides bickered and blamed for more than a week over Obamacare, the president's signature health care law. House Republicans insisted the spending bill include anti-Obamacare amendments. Senate Democrats were just as insistent that it didn't.
Federal employees who are deemed essential will continue working. But non-essential employees will be furloughed.
Most furloughed federal workers are supposed to be out of their offices within four hours of the start of business Tuesday.
As shutdown deadline nears, ping pong on funding continues
(CNN) It's been 17 years since the last government shutdown. The next one is probably just minutes away.
A shutdown appeared certain Monday night as House Republicans acknowledged they can't overcome Senate objections to a proposal that includes provisions aimed at derailing Obamacare.
The plan now is to have another vote that would request a conference with the Senate to work out their differences. The move, which would not avert a shutdown, was slammed by Senate Majority Leader Harry Reid.
He rejected the House's proposal to meet, saying "we will not go to conference with a gun to our head."
For the second time Monday, the Senate rejected a House Republican effort to derail Obamacare tied to a proposal that would avert the shutdown.
The Senate voted to table amendments that would have delayed the individual mandate in the health care law and eliminated health insurance premium subsidies for members of Congress, their staffs and the president.
In the latest volley of legislative ping pong over a short-term spending plan needed to avoid the shutdown, House Republicans were expected to meet to discuss their next steps.
"The government is going to shut down ... I don't know for how long," GOP Rep. Devin Nunes of California told CNN while leaving Speaker John Boehner's office.
Democratic Rep. Chris Van Hollen said the reason there isn't a budget is because Republicans refused to negotiate months ago.
"They want to go to conference with 45 minutes left," Van Hollen said late Monday night. "That is a recipe for a government shutdown,"
Earlier, Senate Democrats had rejected a House proposal by a 54-46 vote on strict party lines.
President Barack Obama made a previously unscheduled statement to reporters on Monday afternoon, blasting the attempts by House Republicans to undermine Obamacare that he said threaten to harm the economy with a shutdown.
"You don't get to extract a ransom for doing your job, for doing what you're supposed to be doing anyway, where just because there's a law there that you don't like," the president said.
Obama later called Boehner and other party leaders in the House and Senate, the White House said, but a Boehner spokesman indicated there was no breakthrough.
Moderate GOP revolt against Boehner?
GOP sources told CNN that moderate House Republicans were trying to galvanize what would amount to a rebellion against Boehner and their tea party colleagues by defeating the latest proposed spending plan with attached anti-Obamacare provisions.
However, a procedural vote on the measure passed with only six Republicans voting "no."
Without congressional approval of new spending legislation, parts of the federal government will begin shutting down when the current fiscal year ends at midnight, forcing agencies to furlough thousands of workers and curtail some services until there is a resolution.
"I feel sad about it. We expect more from our Congress," said Vick Temple, a worker for the Federal Aviation Administration who told CNN he faced being furloughed in a shutdown.
Polls show public opposition to a shutdown, and stocks ended lower Monday on Wall Street due to concerns over the economic impact.
Meanwhile, the two parties persisted in blaming the other side as the shutdown deadline neared.
Photos: Key players in the shutdown debate Photos: Key players in the shutdown debate
Lawmakers back and forth on shutdown Government shutdown looms Political effect of a government shutdown
Republican Rep. Renee Ellmers of North Carolina said on CNN's "New Day" that her party continues to be deeply concerned about Tuesday's scheduled opening of Obamacare health insurance exchanges and "keeping the checkbook out of Barack Obama's hands and the damage can be done there."
Get up to speed on the showdown
Rep. Debbie Wasserman Shultz, D-Florida, appearing alongside Ellmers, characterized the Republican strategy of tying overall government operations to at least a delay in health care changes as "irrational."
"It jeopardizes the economy and it makes no sense," she said.
On Monday morning, Obama told reporters he wasn't resigned to a shutdown, but he signaled its likelihood even as he indicated possible talks with congressional leaders.
"I suspect that I will be speaking to the leaders today, tomorrow and the next day," Obama said at a joint appearance with visiting Israeli Prime Minister Benjamin Netanyahu, who acknowledged the Washington brouhaha by thanking the president for meeting with him "on what I know is a very busy day for you."
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