* Downgrades Erste, RZB and Bank Austria
* Applied one-notch negative adjustment for the banks
* New law causes uncertainty over state support, S&P says (Adds background, detail)
FRANKFURT, Aug 13 (Reuters) - Ratings agency Standard & Poor's has downgraded three systemically important Austrian banks - Raiffeisen Zentralbank Oesterreich, Erste Group and Unicredit Bank Austria - in response to new bail-in legislation.
In a statement on Wednesday S&P said its move follows the July 31 imposition of a law that will wipe out the claims of subordinated debt holders in nationalised bank Hypo Alpe Adria despite a debt guarantee from the State of Carinthia.
The Austrian government's decision to impose losses on Hypo's subordinated debtholders indicates that the authorities' stance towards supporting systemically important banks is wavering, S&P said.
"In our view, the new law indicates reduced predictability of extraordinary government support for systemically important banks, and for banks' hybrid capital instruments and grandfathered debt, than we previously envisaged," S&P said in a statement on Wednesday.
"The negative outlooks on three banks reflect our view that the likelihood of state support could diminish further, as well as bank and industry-specific factors," S&P added.
S&P applied a one-notch negative adjustment to its ratings on the three banks.
It lowered the long and short-term counterparty credit ratings of Erste Group Bank to A-/A-2, from A/A-1, and of Raiffeisen Zentralbank Oesterreich to A-/A-2 from A/A-1.
S&P also lowered the long-term counterparty credit rating on UniCredit Bank Austria to BBB+ from A-, while affirming the A-2 short-term rating.
The outlook on all three banks is negative, S&P said.
Reporting by Edward Taylor; Editing by David Goodman