Democratic vice presidential nominee Joe Biden's son Hunter has stopped working as a federal lobbyist, work that had made him a Republican target in the presidential contest.

"I no longer expect to act as a federal lobbyist," Hunter Biden said in a letter to the Clerk of the House and the Senate Office of Public Records. The letter is dated Aug. 25 and was made public Friday.

Presidential candidate Barack Obama, who chose Biden as his running mate last month, has been a vocal critic of rival John McCain's ties to lobbyists. In a television ad Friday, Obama repeated criticisms of McCain for having current and former prominent lobbyists on his campaign staff.

Obama has refused to accept contributions from federal lobbyists, though some have advised his campaign.

Hunter Biden and his lobbying firm, Oldaker, Biden & Belair, have represented colleges and hospitals, mainly in an effort to secure money for them in appropriation bills. In June, however, Biden also signed on as a lobbyist for a law firm that represents a billionaire couple who run an Internet gambling business. The lobbying documents on file with the Senate Public Records Office show that Biden intended to lobby on the "legality of internet gaming" and the Unlawful Internet Gambling Enforcement Act, which Congress passed in 2006.

The law firm, Sharp & Barnes, represents Russell DeLeon and his wife Ruth Parasol, according to lobbying records. The couple was listed as having a net worth of $1.8 billion in 2006 and made the Forbes top billionaire's list. They dropped out of the list the following year. Forbes reported that a congressional crackdown on online gaming caused their company stock to fall 75 percent.

Biden's letter ending his lobbying work was first reported Friday by The Wall Street Journal's Washington Wire.

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