Stephen Lynch is supportive of the Keystone XL oil pipeline, and Thomas Steyer is not happy about that.

Lynch is the Bay State representative running against fellow Democrat Ed Markey in the upcoming primary election for the U.S. Senate seat vacated by Secretary of State John Kerry. Steyer is a Bay Area hedge fund billionaire who has vowed to pit his significant personal financial capability against Lynch and the Senate hopeful’s support of the pipeline.

“Last month, [Steyer] burst onto the scene with a sharply worded threat to Lynch, warning him that if he did not change his mind and oppose the proposed Keystone XL oil pipeline ‘by high noon on Friday,’ he would launch an aggressive campaign to defeat him in the April 30 primary,” reports the Boston Globe.

With a net worth totaling $1.4 billion, Steyer, a founder and managing partner of Farallon Capital Management, ranks 347th on the Forbes 400.

“He has poured $400,000 into the Massachusetts race so far,”continues the Globe, “bankrolling planes with banners, trucks with video screens, and canvassers who plan to knock on 300,000 doors statewide.”

According to a comparison conducted by Progressive Massachusetts, Lynch has voted almost identically to Markey on issues concerning the environment over the past several years.

In the matter of election finance, The Progressive Mass scorecard also shows both Lynch and Markey supporting “campaign finance reform banning soft-money contributions” in 2002, as well as “requiring lobbyist disclosure of bundled donations” in 2007.

While Steyer is an outspoken opponent of the Keystone pipeline and proponent of environmental issues, he has not been as aggressive in voicing his opinion on campaign finance reform.