When the protests known at Occupy Wall Street began last month, those involved were portrayed as disaffected young people with no organization, no leadership and no demands or objectives. While much of that characterization is accurate, the movement is spreading a message of frustration that resonates with millions of Americans.

The protesters often call themselves “the 99 percenters,” referring to the dramatic income disparity between the very wealthy corporate elite on Wall Street and the average working person.

To its credit, Occupy Wall Street has tried to remain nonpartisan, suggesting Republicans and Democrats are equally at fault in catering to Wall Street’s deep-pocket interests.

In recent days, labor unions have joined the group, claiming solidarity. While it might be true that they share some common complaints, the Occupy Wall Street movement risks its credibility if it allows Big Labor to hijack its message. If organized labor becomes the face of Occupy Wall Street, the group’s broad appeal will be lost, and it will be seen as an arm of a powerful special interest group.

Most of the frustration now vented by protesters crosses party lines. Of the 99 percent who are not Wall Street investment bankers or highly paid CEOs, there are millions of Democrats, Republicans and Independents.

Middle-class people from both major parties as well as Independents understand that while many of them are suffering in this economy, people in the top-floor offices on Wall Street and in much of corporate America are not feeling the pinch.

Some observers see the Occupy Wall Street movement as the liberal version of the tea party, which is associated with conservative politics. That’s a reasonable view — both groups express frustration with the economy and government. But their perspectives and philosophical roots are very different.

There is some overlap in that both groups are unhappy with the influence of money in politics that finds many members of both parties catering to big campaign contributors over regular citizens who have no lobbyists.

While associated with the left, many Occupy Wall Street protesters are bipartisan in their frustration. Many blame President Barack Obama for coddling the big Wall Street banks even while he sometimes talked tough during the mortgage crisis. They also fault him and congressional Democrats for allowing financial reforms, like addressing “too big to fail,” to be watered down and for not pushing for tougher financial regulations to prevent another crisis. Some see the influence of Wall Street as being just as great in the Obama administration as it was in the Bush administration.

The American middle class, often credited with fueling this country’s economic and cultural surge in the second half of the 20th century, is being squeezed by rising costs — particularly health care and education costs — that are increasing far more rapidly than salaries and wages.

The squeeze on millions of Americans’ family budgets, stock market declines and the weak housing market have produced what some analysts are calling a lost decade. And while the middle class has suffered a lost decade, most of the very wealthy are doing better than ever, a fact revealed in the historically wide income disparity in the United States today.

The combination of the lost decade, along with persistently high unemployment, is fueling much of the frustration being expressed by the Occupy Wall Street crowds that are growing and have spread to a dozen cities. That frustration is shared by millions of Americans who will not show up at public demonstrations.

Politicians in Washington should recognize that frustration and work to help the middle class, reduce income disparities while increasing fairness and economic opportunity. Lawmakers should also see that the financial sector is held responsible. Failure to act could see Occupy Wall Street grow to have political influence similar to the tea party’s, but possibly less one-sided — as in vote out incumbents of both parties.

The protests might lead to change. Even if the odds are long, it’s even less likely to happen if the protests are taken over by Democratic politicians and Big Labor. For now the message resonates in a largely nonpartisan way. Occupy protesters should keep it that way.