Wells Fargo & Co. (WFC - Get Report) , the U.S. bank struggling to contain the fallout after being hit by the Federal Reserve with an unprecedented ban on further growth, had its credit rating cut by Standard & Poor's.

The rating was lowered to A- from A, S&P said Wednesday in a statement. The outlook is "stable," indicating no further cuts are currently contemplated.  

S&P took the action after the Fed last week sanctioned Wells Fargo over aggressive sales practices toward its own customers, including opening millions of unauthorized accounts in their names and charging them for car insurance that wasn't needed.

The new credit rating at Wells Fargo is still in the upper tier of S&P's scale for investment-grade bond issuers, so the cut may have little immediate effect. But it's a sign that the scandal is taking an incremental toll on the bank's creditworthiness and could push up its borrowing costs slightly, in an industry where analysts scrutinize even tiny changes in interest rates.     

"Regulatory risk for Wells is more severe than we previously expected, and the process for improving its governance and operational risk policies may take longer," S&P said. "At the same time, the company may be subject to prolonged reputational issues."

Wells Fargo CEO Tim Sloan estimated last week that the growth ban -- a cap on the bank's assets at the current level of about $2 trillion until regulatory conditions are satisfied -- could mean $300 million to $400 million in lost net income this year.

Those costs add to big fines and settlements the bank has already paid to resolve the sales-practice issues since the scandal exploded in 2016, including a $185 million fine imposed by the Consumer Financial Protection Bureau and other regulators. 

The troubles have sapped shareholder returns, with the bank's stock price up just 2.5% over the past year, even as larger rival JPMorgan Chase & Co. (JPM - Get Report)  surged 31%. On Wednesday Wells Fargo shares rose 1.3% to $58.02 in New York trading.  

S&P said it expects Wells Fargo to meet the conditions of the Fed's order and that it will maintain competitive positions in key businesses. That said, the rating could be lowered if the bank fails to get the asset cap lifted "in a reasonable timeframe," according to the statement.  

"Our stable outlook assumes that the company will meet the requirements of the regulatory consent order while maintaining solid market shares in its major businesses as well as a strong financial profile," S&P said.