A group at the forefront of opposition to the Keystone XL oil pipeline and a deep-pocketed environmentalist are warning pro-Keystone Democrats that their position could draw them opposition in 2014 primary races.

The political arm of 350.org recently made its first-ever endorsement, backing Rep. Edward Markey (D-Mass.) over Rep. Stephen Lynch (D-Mass.), a pipeline supporter, in the upcoming special election to replace former Sen. John Kerry (D-Mass.).

Hedge fund billionaire and environmentalist Tom Steyer and young activists have also jumped in, going after Lynch over his Keystone backing. Now, 350 Action and an aide to Steyer say involvement in other primaries could be in the offing.