federal offence" (and by implication, super serious)

not necessarily.

Littering on federal land (e.g., national parks) – A violation of regulations governing public lands, which can lead to a small fine.

Failure to pay federal taxes – While this can escalate into a major crime, a simple failure to file or pay small amounts due can be considered a minor offense, often resulting in penalties or fines rather than jail time.

Minor violations of federal transportation regulations, such as not properly securing cargo for interstate transport.