The US government is seeking a bill that will oblige citizens to enter and leave the US "monetary instruments" with a total value of more than $ 10,000. If a citizen fails to comply with this obligation, imprisonment of up to 10 years and confiscation of the monetary instruments are in discussion.
Since cryptocoins can be traded with a smartphone, they would currently fall under the definition of the term "monetary instruments". The US government is also struggling against our cash and digital currencies.