The Securities and Exchange Commission unanimously voted Tuesday to require large trading firms to identify themselves, so their market activities can be tracked.

The adoption of its long-debated “large trader” reporting rule means any person who trades more than two million shares or $20 million worth in a single day must identify themselves and obtain an ID code for tracking purposes.

Also required to identify themselves will be persons who trade 20 million shares or $200 million during any calendar month.

Market participants have said it will be "hugely challenging" to comply with the rule.