Reuters has obtained a Treasury Department document that details giving intelligence agencies more access to financial information than ever before. Banks are already responsible for collecting and reporting information on suspicious transactions and passing that along to the FBI. Other intelligence agencies, though, like the CIA, have to specifically request that data on a case-by-case basis. The new Obama administration plan would change that, and instead give all U.S. intelligence agencies access to the same giant set of data the FBI already has.
Using financial records to catch criminals is an American tradition. Prohibition-era gangster Al Capone was famously caught for tax evasion after the Treasury Department pored over his financial records. The FBI has used financial data to track and freeze al Qaeda assets. The famous criminals caught or hindered this way are probably what the Obama administration wants people to have in mind when expanding access to this database.
The problem is that suspicious actions aren't the same thing as illegal actions, and while it's certainly unusual for someone to pay for something with $10,000 cash, it isn't inherently illegal, and there's a chance that something perfectly legal, just eccentric, gets flagged in this database. With just the FBI having access, that's a negligible risk, but with every intelligence agency working with the data, the chance of someone getting it wrong increases. This is always a problem when privacy protections are removed. Given past experience with over-broad and shared government lists of suspicious people, don't expect this to function smoothly.