Turkey is signaling a major shift in its approach to cryptocurrencies as parliament prepares to debate over a landmark bill that would see the imposition of new levies on digital asset trading—a move that would put investors’ portfolios under fresh scrutiny.

The tabled bill, introduced by the ruling Justice and Development Party (AK Party), is an amendment to the Income Tax Law and Expenditure Taxes Law, and represents the government’s most ambitious effort yet to formalize the country’s…