A tiny wealthy male elite is behind most of the biggest contributions to the 2012 election cycle in the US, a new study shows. The report comes just as the US Supreme Court considers whether it should strip a ceiling on political donations.

In a case the Supreme Court will begin hearing next Thursday, Shaun McCutcheon, a wealthy donor backed by the Republican National Committee, is challenging this aggregate limit on how much an individual may donate overall to candidates, parties and political action committees (PACs) over an election cycle.

If the court strikes down the limit, it could prompt bigger contributions from those who already reached or were about to reach it, argues Public Campaign, a Washington-based advocacy group. Such a move would “put power even further into the hands of Wall Street bankers, billionaires, and K Street lobbyists,” it says.

The group analyzed campaign finance records and census demographic data to paint a likely portrait of those limit-restricted donors. The study included only individuals and not corporations, unions and other groups. The resulting portrait is that of a wealthy white male, possibly a billionaire from Wall Street or an influential lobbyist from K Street, the group says.

The Public Campaign says that 1,219 individual donors gave at least $105,300 – within 10 percent of the $117,000 aggregate limit – in 2012 campaign. Three of the five richest Americans – Larry Ellison, Charles Koch and David Koch – and one in every six US billionaires gave up to the contribution limit. Their donations totaled more than $150 million, with 56 percent going to Republicans and 41 percent to Democrats and the rest to independents and PACs, the study showed.

More than 80 per cent of the elite donors come from America’s richest 10 percent of neighborhoods as measured by per capita income. Wall Street and the financial sector dominate the ranks, accounting for 28 percent of the donors, the study says. One tenth of them are lawyers or lobbyists.

Less than one-in-50 of the top donors live in communities which are predominantly African-American or Hispanic, the study showed. Only about one quarter of the elite donors are female.

"You're going to end up having politics be e-Bay for millionaires and billionaires," said Nick Nyhart, president and chief executive of Public Campaign in a reference to the popular online shopping service.

But former Federal Elections Commission Chairman Brad Smith said worries about a small group of people having disproportionate influence are unfounded.

"Historically, this is how campaigns have always been funded. A handful of people, from their personal fortunes, kept the revolution going," he told Reuters.

Smith’s Center for Competitive Politics has filed an amicus brief in the case arguing against the contribution limits.

The 2012 election cycle was the most expensive on record, according to Washington research group The Center for Responsive Politics. It featured more than $6 billion in spending across federal campaigns.