But unlike most private foundations, Mr. Baca’s gets little of its money from its founders’ pockets. Instead, local companies and major corporations that have often turned to Mr. Baca’s Washington office for help, and usually succeed in getting it, are the chief donors.

A review by The New York Times of federal tax records and House and Senate disclosure reports found at least two dozen charities that lawmakers or their families helped create or run that routinely accept donations from businesses seeking to influence them. The sponsors  AT&T, Chevron, General Dynamics, Morgan Stanley, Eli Lilly and dozens of others  contribute millions of dollars annually in gifts ranging from token amounts to a check for $5 million.

Since 2009, businesses have sent lobbyists and executives to the plush Boulders resort in Scottsdale, Ariz., for a fund-raiser for the scholarship fund of Representative Steve Buyer, Republican of Indiana; sponsored a skeet shooting competition in Florida to help the favorite food bank of Representative Allen Boyd, Democrat of Florida; and subsidized a spa and speedway outing in Las Vegas to aid the charity of Senator John Ensign, Republican of Nevada.

Just last month, they touted their largess with flags bearing their names near the tees at a golf tournament benefiting the foundation of Representative James E. Clyburn, Democrat of South Carolina.

Despite rules imposed in 2007 to curb the influence of special interests in Congress, corporate donations to lawmakers’ charities have continued, thanks to a provision that allows businesses to make unlimited gifts to them. And while business executives say they want to give to a good cause, their pattern of spending  contributions that often are not disclosed, in apparent violation of ethics rules  suggests another reason.