An arbitration hearing of the International Tennis Federation (ITF) said on Thursday that Bedene, 27, remained ineligible because he has already represented Slovenia three times in the team competition.
The ITF introduced the new rule in 2015, shortly before Bedene became a British citizen.
"The ITF change in rules has come at precisely the wrong time for him," said Charles Hollander QC, who led the hearing. "Bedene cannot be characterised as one of those players who desire to adopt a 'flag of convenience'."
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Bedene's initial appeal against the ban was turned down by the ITF's board last March. Since then, he has fallen to outside the top 100 in the ATP rankings.
While the decision is a blow for Bedene, 2015 champions Britain are in good shape and beat Canada in the World Group first round, even without Wimbledon champion Andy Murray.
(Reporting by Martyn Herman, editing by Larry King)
