Moody's cut four banks' credit ratings. Reuters / Brendan McDermid

Moody’s Investors Service (MCO) downgraded four of the biggest U.S. banks after its researchers determined the government would be less likely to help them repay creditors in a crisis.

The four banks, Morgan Stanley (MS), Goldman Sachs Group Inc. (GS), JPMorgan Chase & Co. (JPM) and Bank of New York Mellon Corp. (BK), saw their senior holding company ratings lowered one level Thursday, Bloomberg reported.

Bank of New York was cut to A1 from Aa3, Goldman Sachs was lowered to Baa1 from A3, JPMorgan was cut to A3 from A2, and Morgan Stanley was downgraded to Baa2 from Baa1.

BNY Mellon, Goldman Sachs, JPMorgan and Morgan Stanley saw their subordinated debt ratings lowered as well.