WASHINGTON  Among the thousands of demonstrators who jammed the Wisconsin State Capitol grounds this weekend was a well-financed advocate from Washington who was there to voice praise for cutting state spending by slashing union benefits and bargaining rights.

The visitor, Tim Phillips, the president of Americans for Prosperity, told a large group of counterprotesters who had gathered Saturday at one edge of what otherwise was a mostly union crowd that the cuts were not only necessary, but they also represented the start of a much-needed nationwide move to slash public-sector union benefits.

“We are going to bring fiscal sanity back to this great nation,” he said.

What Mr. Phillips did not mention was that his Virginia-based nonprofit group, whose budget surged to $40 million in 2010 from $7 million three years ago, was created and financed in part by the secretive billionaire brothers Charles G. and David H. Koch.

State records also show that Koch Industries, their energy and consumer products conglomerate based in Wichita, Kan., was one of the biggest contributors to the election campaign of Gov. Scott Walker of Wisconsin, a Republican who has championed the proposed cuts.