"We want our freedom back," former GOP presidential candidate Herman Cain told hundreds of ralliers standing in the rain in Upper Senate Park, a few hundred yards from the steps of the Supreme Court. "That's what this is about, the freedom to choose our own doctors … the freedom to choose our own health insurance plan."
Cain also said that he might not have survived his battle with cancer under the new law had "some bureaucrat" learned he had only a 30 percent chance of survival.
"Stay inspired," he said, urging the crowd help defeat Obama in November.
"ObamaCare is a cancer in our government, and we’re going to rip it out," said Jenny Beth Martin, national coordinator of the Tea Party Express which sponsored the "Road to Repeal" rally.
The rally largely marks the big return to Washington for the Tea Party, a loose organization of grassroots groups that helped conservative Republicans take over the House in the 2010 wave election.
"The Tea Party is back," shouted Jim Hoft of the Gateway Pundit Blog.
The high court will begin hearing argument Monday on the Patient Protection and Affordable Care Act, passed by Congress in 2010.
The legislation is intended to provide health insurance to more than 30 million previously uninsured Americans.
However, opponents say the law is unconstitutional, largely because Congress does not have the power to force unwilling Americans to buy health insurance or pay a fine. They are also concerned about how the legislation will increase costs for the federal government, doctors and those who already have insurance.
Congressional Budget Office now projects the legislation will cost $1.76 trillion from 2013 to 2022.
The case was brought before the nine justices by Florida and 26 other states.
The legislation "takes a huge leap toward socialism," Rep. Louie Gohmert, R-Texas, told the Tea Party crowd, including some holding signs that read "Repeal or Revolt." "This is a government takeover masked as a health care bill."
The justices will hear arguments over three days, starting with whether the case was brought before the high court prematurely because nobody has been fined for not having health insurance. Arguments on Tuesday will focus on whether Congress overstepped its authority by requiring Americans to purchase health insurance starting in 2014 or pay a penalty.
Wednesday's arguments will be split into two parts: Justices will hear 90 minutes of debate in the morning over whether the rest of the law can take effect even if the health insurance mandate is unconstitutional and another hour Wednesday afternoon over whether the law goes too far in coercing states to expand the federal-state Medicaid program for low-income people by threatening to cut off federal aid to states that don't comply.
The justices might decide not to rule on whether the law is constitutional but are expected to deliver a decision near the end of Supreme Court session in June.
The Associated Press contributed to this report.