The bank further said Crisil Ratings has assigned a negative outlook to the proposed bonds issue.
"The bank intends to raise capital funds through issuance of tier 2 bonds. In this regard, Crisil Ratings has assigned 'CRISIL AAA' rating with negative outlook to the proposed Basel-III compliant tier-II bond issue of Rs 1,000 crore," it said.
Besides, Union Bank said Crisil has reaffirmed ratings on other debt instruments with negative outlook.
Union Bank stock closed 2.87 per cent higher at Rs 122 on BSE.