It looks like banks are on the way down this morning, as Bank of America (NYSE:BAC) and its compatriots face another round of new allegations of questionable practices. So far in trading, the bank is down 0.26% -- 45 minutes into trading. With another costly issue on its plate, should B of A investors begin to worry that the bank is beyond saving?

Setting the benchmark
Singapore disclosed today that it has censured 20 banks for attempting to rig its benchmark interest rates. Among the 20 are B of A, Citigroup (NYSE:C), and JPMorgan (NYSE:JPM). The banks allegedly bid to set the Singapore Interbank Offer Rate, rates for swap instruments, and currency benchmarks. The Monetary Authority has stated that it will begin taking steps to make rigging of benchmark rates a criminal offense and has ordered the banks to set aside as much as $9.6 billion as it continues its review.

Many countries have stepped up oversight of their benchmark rates since last year's LIBOR scandal. With a $4.7 trillion dollar market, currency trading is prime for manipulation, making it a target for more regulation and oversight. Citigroup, JPMorgan, and Bank of America all play a big role in the U.S. market's trading activity for swaps and currency trading. The three join Morgan Stanley (NYSE:MS) and Goldman Sachs (NYSE:GS) as the banks that control 90% of the swaps/derivatives activity in the U.S.

Enough is enough?
Bank of America has been pummeled by lawsuits and other snafus ever since the financial crisis, and with the newest issue coming from a single international market, there's no telling how many others may follow once further reviews of rates and trades are completed. With banks involved in the LIBOR scandal paying upwards of $2.5 billion for their transgressions, is this new drama for B of A the straw that broke the camel's back?

Long-term investors should have a specific view of the bank -- focusing on the fundamentals of its operations, the knowledge and abilities of management, and the opportunities for the next 5-10 years. But with big hurdles coming at you left and right, it may be hard to escape the overwhelming pressures to drop your investment in the bank.

Putting some numbers to the problem, Bank of America has already shelled out $50 billion in settlements just for its Countrywide-related problems, with another $60 billion on the line. And though there are 20 banks involved in the Singapore rigging scandal, there's no telling how much of the $9.6 billion price tag the authorities have placed on it will be attributed to B of A.

In the end
The bank has already handled a large portion of its legacy issues stemming from the financial crisis, and it's paid dearly for them. But as new issues arise, you'll have to weigh the monetary price of the bank's involvement with your own investment thesis. Determine whether you think the bank is still viable as an operation and if the bottom line can sustain continued hits from problems that are sure to arise down the road.

Fool contributor Jessica Alling has no position in any stocks mentioned -- you can contact her here. The Motley Fool recommends Bank of America and Goldman Sachs. The Motley Fool owns shares of Bank of America, Citigroup, and JPMorgan Chase. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.