Switzerland's upper chamber voted against the draft text and sent it back to the lower chamber for reconsideration, Swiss newswire ATS said.
The upper chamber would reexamine the text in December.
The current draft treaty allows Washington to continue filing requests to Bern for data of suspected tax cheats, even if US tax authorities do not specify the identities of suspects.
Parliamentarians are seeking more information about a more comprehensive deal that is aimed at ending the tax evasion dispute and regularising any untaxed assets held by Americans.
The deal is currently being negotiated between Bern and Washington.
Over the weekend, local press citing unnamed sources said that the deal was close to be concluded.