Denver ? Left-leaning protesters are trying to rally a crowd in the Vail area this weekend as a prominent closed-door conservative meeting gets going.

The billionaire brothers Charles and David Koch (kohk) of Koch Industries are playing host to a semiannual retreat in the Vail area starting Sunday. The retreats are closed to the public and the press, but news of the meeting leaked out when Virginia’s Republican governor, Gov. Bob McDonnell, listed the gathering on his schedule.

That prompted several left-leaning groups in Denver to plan a protest rally in nearby Avon on Sunday, the first day of the retreat. Organizers say they hope several dozen join to protest what they call undue influence on politics by deep-pocket donors such as the Koch brothers.

Koch Industries is based in Wichita, Kan.