CAMBRIDGE, Md. -- President Obama blasted Tennessee Republicans Friday for attempting to block a union vote at an auto plant there, according to a senior Democratic aide.

(AP Photo/Erik Schelzig, file)

Employees at a Volkswagen auto plant in Chattanooga are voting Friday on whether to join the United Auto Workers union. If a majority of workers vote yes, it would mark the first time in nearly three decades of trying that the United Auto Workers has successfully organized a plant for a foreign brand in the United States. The union is poised to collaborate with Volkswagen, which is hoping to establish a German-style "works council" to help manage plant operations.

Obama waded into the brewing fight between conservative groups and labor leaders over "right to work" states during a closed-door exchange with House Democrats during their annual policy retreat, according to the aide, who asked for anonymity in order to speak frankly about the private meeting.

He briefly touched on the subject, saying that people in the region appear to favor the unionization plan, except for local politicians who are "are more concerned about German shareholders than American workers," the aide said.

As The Post's Lydia DePillis reports from Chattanooga, Tennessee's GOP leaders and other conservative activists have publicly worried about the danger of damaging the state's low-cost reputation. Sen. Bob Corker (R), who wooed VW to town when he served as mayor of Chattanooga, has been barnstorming media outlets to warn against giving the UAW a toehold.

Obama raised the subject unprovoked on Friday, in response to a question about extending benefits for long-term unemployed workers from Rep. Jan Schakowsky (D-Ill.), according to the aide. She had asked the president how he might be able to help Democrats push for an extension of the benefits.

Obama said he is working with Democrats on the issue but that there is no "administrative recourse," the aide said.

"I haven't been shy about making this an issue," the president said, adding later that he is "open to additional strategies people may have out there."