There are multiple definitions - click on the translation that matches your context.

Código Tributário Nacional (CTN)

substantivo próprio

full

tax code

noun

Definitions of tax code

a number used by an employer or pension provider to calculate the amount of tax to deduct from your pay or pension

If you have the wrong tax code you could end up paying too much or too little tax.

the set of laws concerning tax

The dispute concerns the meaning of the word "directly" within Tennessee's tax code.