IDBI, which is readying for a merger with IDBI Bank, may have to revise its $500 million external commercial borrowing proposal after the government tightened the norms last week. It, however, plans to tap the domestic market by November end with its tax-saving bonds targeted at raising upto Rs 3,000 crore.Although the government is discouraging ECBs above $100 million, the finance ministry had earlier cleared ICICI Bank’s $300 million ECB as the bank would use it for ailing steel companies.The bonds and ECBs are crucial for IDBI as it would continue with developmental financing even after Parliament approves the bill to repeal the IDBI Act. ‘‘The first tranche of bonds are slated to hit the market during November end subject to regulatory approval,’’ sources said. ‘‘As soon as the clearance comes, the bonds would be launched,’’ the officials said. IDBI had applied for raising $500 million through the external commercial borrowings route this fiscal for restructuring debts of steel and textile companies.