Sen. Jon Tester (D-Mont.) dropped out of a League of Conservation Voters fundraiser in New York last night in the wake of criticism from his challenger Rep. Denny Rehberg (R-Mont.), citing a scheduling conflict.

Tester campaign spokesman Aaron Murphy defended the senator's cancellation, pointing to a publicly available schedule. That document shows Tester scheduled to attend an Indian Affairs Committee hearing following the Senate vote that ended at 3 p.m. yesterday. His scheduled also indicates that at 4 p.m. he was to record a "holiday greeting for the troops."

Rehberg launched an attack on the Democrat's scheduled appearance at the New York dinner earlier this week and called for him to drop out of the fundraiser, describing LCV as an "extremist" group because of its opposition to the proposed Keystone Xl pipeline.

Rehberg’s campaign spokesman Chris Bond reiterated that criticism today, stating: "It's clear that this was a desperate last-ditch effort by Senator Tester to save his own political hide, and folks in Montana won't be fooled by his decision to suddenly run away from the same anti-job environmentalist groups he consistently sides with in Washington."

"It's time for Tester to stop hypocritically playing politics and start convincing his radical environmentalist supporters and his allies in the Obama administration to stop standing in the way of Montana jobs," Bond added.

Rehberg's campaign contends that construction of the 1,700-mile pipeline, which has been pushed back as the Obama administration continues to examine a proposed route, would generate $7.5 million in revenue for Montana and create new jobs.

Tester has said he supports the pipeline's construction, so long as private property owners' rights are protected.

Murphy pushed back against the GOP criticism about the LCV fundraiser.

"The [National Republican Senatorial Committee] should spend less time trying to schedule Jon Tester and more time encouraging Congressman Dennis Rehberg to update his own online schedule, which he has failed to do. Dennis Rehberg has once again failed to be accountable to the Montanans he's supposed to serve," Murphy said.

Rehberg posts his schedule to his House website, but it has not been updated since Dec. 2.