Labor unions, hot for immigration reform and worried about Democratic control of the Senate, are doubling down on the 2014 midterm elections, boosting donations to their super PACs to levels that best New York Mayor Michael Bloomberg’s contributions to moderates and Jonathan Soros’ to liberal interests.

During the first half of 2013, unions contributed $10 million to their political arms, more than five times the $1.7 million coughed up during the first half of 2011, the last off-year election period, according to the independent Center for Public Integrity.

The group that investigates political money found three unions among the top seven political donors for the period, with the United Brotherhood of Carpenters and Joiners of America the leader at $1.9 million. The AFL-CIO was second among labor, at $1.8 million, and the American Federation of State, County and Municipal Employees the third biggest spending union at $1.5 million.

The Carpenters funded its super PAC, Working for Working Americans: the AFL-CIO invested in its own super PAC, Workers’ Voice.

In a media roundtable last week, AFL-CIO President Richard Trumka said he planned to spend freely in the midterm elections and would focus on Texas and also “build a firewall” around the Democratically-controlled Senate, which is in jeopardy of falling into Republican hands.

“We’ll be involved at the state level, county level and district level, playing in some states where we haven’t in the past,” Trumka said at the event hosted by the Christian Science Monitor. “Obviously, the Senate is important. We will build a firewall around the Senate like we did in the last election to protect progressive candidates,” Trumka said. “The House is very important too because the only thing standing between us and immigration reform is [House Speaker] John Boehner and House Republicans.”

The Center’s report found that union giving accounted for roughly $1 of every $6 raised by super PACs in the first half of 2013.

The top donor was the Democratic Governors Association at $3.58 million. Bloomberg gave $2.25 million during the period, Soros $1 million.

The spending also shows that liberal groups are catching up to conservative groups in super PAC funding.

Paul Bedard, The Washington Examiner's "Washington Secrets" columnist, can be contacted at