The mandate hinges on the idea that there are more healthy people in the world than sick people.
By requiring all of the healthy people to have health insurance, whether they need it right now or not, their premiums will help balance out all the unhealthy people who are racking up lots of hospital bills.
That, in theory, would keep health insurance premiums and healthcare costs low for everyone.
Many have claimed the mandate was unconstitutional, but the U.S. Supreme Court released an opinion last year upholding the provision.
Manchin's opposition to the individual mandate is not surprising.
While running for Senate in 2010, Manchin told the Wheeling Intelligencer newspaper he would support a repeal of the health care law "unless we can find common ground and common sense."
About two years ago he told ABC News he didn't like the individual mandate because it forced citizens to purchase health insurance.
"I've always had a concern and a problem with the mandate, that we were forcing it, basically saying by the law of the land you have to buy the product," he said at the time.
On Thursday morning, Manchin appeared ready to break ranks with his fellow Democrats and support a bill that would prevent a government shutdown while delaying the mandate.
"There's no way I could not vote for it," Manchin said, according to Bloomberg Businessweek. "It's very reasonable and sensible."
Manchin, speaking at a Bloomberg Government breakfast on Thursday, said President Barack Obama's administration already has given businesses until 2014 to provide health insurance for employees.
"Don't put the mandate on the American public right now," Manchin said, according to Bloomberg. "Give them at least a year. If you know you couldn't bring the corporate sector, you gave them a year, don't you think it'd be fair?"