Twenty-five people have been arrested for trespassing during a protest demonstration outside of a retreat where the secretive billionaire Koch brothers held an assembly for conservative elected officials, political donors and strategists.

Hundreds of liberal activists, environmentalists and union members protested outside the Rancho Las Palmas Resort in Rancho Mirage, California to protest against what they view as the heavy financial influence of the Koch brothers in conservative causes.

Koch spokeswoman Nancy Pfotenhauer said the closed-door meeting brings together some of America's greatest philanthropists and job creators … who share a common belief that the current level of government spending in our nation is simply unsustainable.

Widely associated with the Tea Party fringe of the Republican Party, the Koch brothers have come under unprecedented media scrutiny in recent years.

Protestors carried placards condemning corporate greed, chanted slogans and moved toward a barricaded police officers at the entrance of the a resort.

The two brothers control Koch Industries, the second-biggest privately held company in the country, and have financed endeavors agitating for limited-government and also contributed $1-million to failed initiative to suspend California's law to reduce greenhouse gases.

In decades past, the Koch family has supported conservative organizations and campaigns, including significant funding for the Cato Institute, the Heritage Foundation and the U.S. Chamber of Commerce.

According to media reports, Cathy Riddle, a Temecula, Calif. website developer who held a sign reading Corporations are not people” at the rally, said We cannot have democracy unless everyone has a voice.”

Donors like the Koch brothers are drowning us out. Their voices are louder, she added.

One group that one of the brothers, David Koch, helped form, Americans for Prosperity, was cited by President Obama as an example of special-interest money that went into last year's mid-term elections.

Bob Edgar, president of Common Cause and a former Democratic congressman, warned the rally that the Koch brothers are at the center of a hard-core conservative political network that wants to erode consumer protections and compromise fair elections.

This is a fight for nothing short of the heart and soul of America, he said.

“This is a critical moment for us,” Mary Boyle, vice president for communications at Common Cause, told the New York Times. “The Koch brothers embody this ability to tap vast corporate profits and influence policies that undermine the public welfare.”

However, conservatives defend the Koch brothers.

Grover Norquist, president of the conservative Americans for Tax Reform, who has attended Koch meetings in the past, said Common Cause pretends to be in favor of political engagement and free speech, and now they are shouting down a group that wants to be engaged.”

The Koch brothers encourage people to get involved in politics, support think tanks, to start think tanks. It's important work, he added.