Of the 10 organizations donating the most to political super PACs for the 2014 election, seven favor liberal groups. They have spent a combined $58 million in the current election cycle.

By contrast, only two of the top 10 favor conservative groups, sending them about $8 million. The remaining top 10 donor, the National Association of Realtors, favors neither.

That's according to new figures compiled by the Center for Responsive Politics. The list isn't comprehensive because groups organized as 501(c)4 nonprofits are not required to disclose their donors. Still, it refutes the widely held assumption that conservative sources are the ones spending the really big money to influence voters.

Super PACs are political action committees that are allowed to raise unlimited sums of money and spend it to directly influence elections. They are relatively new, having been first been allowed in 2010.

Topping the center's 2014 list is liberal philanthropist Tom Steyer, who has given more than $20 million, all of it to liberal groups. That beats the nearest runner-up by $10 million.

Another heavy hitter is the Democratic Governors Association, at No. 3, which has donated $8.1 million, while the Republican Governors Association weighs in at No. 15, having donated only $2.7 million.

Three of the top 10 donors are Big Labor groups: The Carpenters and Joiners Union ($7.2 million), the National Education Association ($6.5 million) and the AFL-CIO ($5.4 million). With the exception of $250,000 the Carpenters sent to right-leaning groups, all of the money went to liberal groups.

Three other Big Labor groups made the top 20: The American Federation of State, County and Municipal Employees ($3.1 million), the United Steelworkers ($2.8 million) and the United Association of Plumbers and Fitters ($1.8 million).