Another beauty from Lyn:
In 1970, Congress passed the Bank Secrecy Act, which made banks file reports to the government whenever their customers do more than $10,000 in transactions within a day. Back then, this dollar amount was worth more than the median annual income, and reporting therefore happened rather infrequently. However, the Bank Secrecy Act was not adjusted for inflation, and so over the course of five decades the government has automatically reduced the threshold for necessary reporting and has therefore continually expanded their surveillance mandate each year without further legislation.
The combination of restricting the number of physical banknotes in circulation, making it undesirable to hold physical banknotes for long periods of time due to inflation without interest, and surveilling bank deposits, has been an effective surveillance and control combination.