In asking the judge to uphold the Metro regulation, Pett said the authority's ban on commercial activity is aimed at preserving clear access for the 500,000 passengers who ride the Metro each day.
"To permit commercial activity would most likely result in persons obstructing ingress and egress to the stations by selling their wares and by spreading out on the sidewalk, as [Young] has done and proposes to do with his guitar case," she said.
"Plaintiff has ample avenues of communication available to solicit money from persons by word or deed, other than on WMATA property," Pett said.
Read MoreArtist sues over 'Angry Birds' royalties
Young's lawsuit is being funded by the non-profit civil liberties group, The Rutherford Institute.
"America's founders ensured that expressive activities, no matter what the medium – whether it's spoken, written, sung, painted, or played – are clearly protected by the First Amendment," Rutherford Institute President John Whitehead said in a statement.
"At a time when the government spies on its citizens, monitors their activities, treats them like suspects, and denies them fundamental rights, it's not surprising that the government would clamp down on free speech activities, even of the musical variety," Mr. Whitehead said.
"If we are to have any hope of salvaging our freedoms, it is more critical than ever that we stand up for the rights of those who dare to speak up and challenge the status quo, whether they be artists, activists, or government whistleblowers," he said.
—By Warren Richey, The Christian Science Monitor