I currently have a billing dispute regarding my credit card. While the dispute was under investigation, the bank reported my account negatively to the credit-reporting agencies. Can it do this?
No. Generally, if you have filed a proper billing error dispute, the bank shall not make (or threaten to make) an adverse report to any person about your credit standing.
The bank also should not report that an amount or account is delinquent because you failed to pay the disputed amount—or related finance or other charges—while the investigation proceeds.
However, the creditor can still make an adverse report if you have failed to pay any portion of the undisputed amount due.
If the bank is a national bank and you want to file a complaint with the OCC, visit the OCC complaint page.