WASHINGTON - A crowd of about 100 progressive and liberal activists rallied outside the White House this afternoon to express outrage over the recently released Obama administration budget plan that would cut Medicare and Social Security benefits.

The rally, organized by left-wing organizations including MoveOn.org and the Progressive Change Campaign Committee and attended by lawmakers including Sen. Bernie Sanders, was held in protest over the proposal to create a chained Consumer Price Index - or CPI - included in the White House budget, which could mean lower Social Security benefits for millions of senior citizens and veterans.

The chained CPI proposal could lead to slower growth of Social Security benefits in the next few years because it would determine benefits using a slower inflation rate. The proposal discussed in the past by House Republicans could lead to the average 65-year-old losing out on $130 a year in annual benefits starting in just three years.

RELATED: Social Security Cut of $130 Per Year Seen In Cliff Proposal

Organizers have formed a coalition to deliver petitions with more than 1 million signatures to the president to prevent the bill from making it to Capitol Hill.

"We want to make sure … this is dead on arrival," Democracy for American chairman Jim Dean told ABC News.

Dean's organization is one of the many progressive groups that are part of the coalition to deliver the petition to the White House. Dean said that although he and his organization appreciate the president's "forceful leadership" on issues like gun violence prevention, the CPI proposal is one that has caused them to be extremely disappointed in him.

"People understand that we are not getting everything out of this person," Dean said. "This was never our way or the highway - even when he was elected in 2008. He's crossed a line here."

Sen. Bernie Sanders, I-Vt., urged President Obama to think twice about the budget plan and said it could only lead to devastating consequences in increasing the wealth disparity between the top 1 percent and the rest of America.

"People who have voted with the president … are extremely disappointed with the president," Sanders told ABC News. "(Americans) are saying do not balance the budget on people who have lost their arms and legs defending this country."

Rally organizers said Obama was doing a disservice to the senior citizens who rely on social security benefit checks to survive.

"We've got to get here now in order to be sure that the voices of people who are going to be impacted by the president's proposals will be heard by him," said Brad Wright, a spokesman for the National Committee to Preserve Social Security and Medicare, which is also part of the coalition. "I can't tell you how disappointed we are - he has said that he would not cut social security … and now they're doing it. That's a pretty serious disconnect."

The budget has yet to take center stage in Washington. Instead, the focus has been on the gun control debate, with some GOP lawmakers threatening a filibuster on gun control legislation.