Democratic House members are being squeezed by pro and anti Keystone pipeline advocates and the issue threatens to throw a monkey wrench into the 2014 mid term election.

The Laborers' International Union of North America (LIUNA) has sent a letter to its members telling them to put some heat on Democratic House members who oppose construction of the Keystone pipeline. But mega-donor Tom Steyer has threatened Democrats with being cut off from his $100 million war chest if they vote for the project.

The issue has pitted activists against each other and has caused President Obama to delay his decision until he can figure out a way out of the mess.

The Hill:

A letter distributed Friday by the Laborers' International Union of North America (LIUNA) to the districts of 27 House Democrats calls for union members to make sure their representative "feels the power and the fury of LIUNA this November."

Their crime: signing a letter to Secretary of State John Kerry last month urging him to reject Keystone, which would carry oil sands from Canada to Gulf Coast refineries.

"Your member of Congress is trying to destroy job opportunities for our LIUNA brothers and sisters," said the letter signed by Terry O'Sullivan, the general president of LIUNA.

"For every action, there is a reaction, and our reaction to this frontal assault on our way of life needs to be loud and clear. If you do not stand with us, we sure as hell will not stand with you," O'Sullivan wrote, noting the jobs Keystone would create for union members.

A copy of the LIUNA letter was obtained by The Hill.

LIUNA also sent letters to the House Democrats directly, dangling the 2014 election threat in front of each member.

The Democrats on LIUNA’s hit list include Reps. Frank Pallone Jr. (N.J.), Anna Eshoo (Calif.), Raúl Grijalva (Ariz.) and Tim Ryan (Ohio).

The Keystone pipeline has long been a source of friction between Democrats and labor unions. While green groups are fighting aggressively to stop the project, many unions support it on the grounds that it would provide a surge of jobs into the construction industry.

The letter to LIUNA members asks them to keep in mind that "unemployed construction workers desperately need the work" generated by the $5.4 billion project, calling it a "lifeline" for thousands of members.

The building trade union said it is committed to reducing greenhouse gas emissions, but not at the cost of jobs.

"The livelihoods of LIUNA members are too important for our union to continue ignoring the actions of supposed ‘friends’ who stand in the way of jobs that enable our proud members to provide for themselves and their families," states a letter to Rep. Jan Schakowksy (D-Ill.), one of the 27 Democrats targeted.

The push by LIUNA underscores the backlash President Obama might face in November if he punts a decision on the oil-sands pipeline past the election.

The decision pins Obama between different factions in the Democratic base.

That other faction is led by former hedge fund manager Tom Steyer who is making no bones about his unhappiness with Democrats who don't toe his extremist green line:

Mr. Steyer, a 56-year-old hedge-fund billionaire, said environmentalists must embrace "hardball" politics. His super PAC, NextGen, attacked Keystone backer Rep. Stephen Lynch in the Massachusetts Democratic Senate primary last year.

On opening day of the baseball season last year, as Mr. Lynch was working the crowd at Fenway Park, Red Sox fans looked up to see an airplane trailing a banner: "Steve Lynch for Oil Evil Empire." Then-Rep. Ed Markey won the primary and subsequent election.

Rep. Lynch, who represents the Boston area, declined to comment through a spokeswoman. During last year's primary, he wrote an article for the Boston Globe calling Mr. Steyer the representative of "a left-wing environmental faction that has adopted the same divisive tactics as other special interests."

A more recent target of Steyer criticism in a NextGen online spot, Sen. Mary Landrieu of Louisiana, is a key to Democrats maintaining their Senate majority in this fall's elections. Her office declined to comment on Mr. Steyer.

Mr. Steyer was welcomed by Democrats when he appeared on the national political scene in 2012. Officials saw him as someone who could mobilize younger voters around climate-change causes and counterbalance Republican energy-industry donors such as the Koch brothers.

But like his GOP counterparts, he doesn't always spend his millions as his party would wish. In private, administration and party officials grumble about Mr. Steyer's activism, in particular his attacks on some Democrats.

The tensions could be on display in coming weeks. The event for the DSCC's Blue Green Council includes Senate Majority Leader Harry Reid of Nevada, according to the invitation. Mr. Reid is banking on Ms. Landrieu's re-election to maintain the Senate Democratic majority.

At the event, Mr. Steyer plans to unveil a poll he commissioned on the popularly of the Keystone, and it probably isn't going to be positive for the pipeline.

Mr. Steyer has indicated he and NextGen will likely get involved this year in the Pennsylvania governor's race, where energy issues are in play, and the Iowa Senate race.

Damned if you do and damned if you don't - not a satisfactory state of affairs for a Democratic politician who needs the cash Steyer can give him as well as the campaign assistance the unions have long given Democrats.

Eventually, Obama is going to have to rule and offend a lot of his supporters. It will probably come down to whose loss of support will do the least amount of damage to Democrats in November.

Not very complicated when you consider that the issue will play into the GOP's hands in several states.