The Inland Revenue Department proposes changing the rules for firms buying equipment overseas using foreign currency.
PwC tax partner Elly Ward says the current system is cumbersome and costly, and needs changing.
She says the proposal is that companies that import or buy equipment from overseas can follow their accounting when they're working out their tax bill that's associated with that equipment.
Ms Ward says it would apply across the board, whether it's a farmer importing a tractor directly into New Zealand or an airline importing aircraft.
She says the current legislation is extremely complex and when imported equipment is bought in a foreign currency it requires a series of complicated, costly calculations.
"What that's meant is that either companies are spending a lot of time and money working out their tax bill, or they're not doing it and they're taking a pragmatic approach that says we'll adopt our accounting and hope that it's near the calculation and we'll be ok".
Ms Ward says the proposed rules are trying to make it simpler for companies when they are buying these pieces of equipment to make their capital decisions.
She says the new legislation has been a long time coming and she hopes it will be in place by the end of the year.
