The Customs Department's ability to stem tax leakage is the crucial factor in recording financial statements accurately and at the heart of the single financial account scheme, Finance Minister Apisak Tantivorawong says.
"If tax leakage still persists at the Customs Department, how can the single financial account achieve its objective?" he asked.
"When some importers understate either prices of imported goods or the volume of products, how can others who do not understate tax liabilities compete?
"If that's the case, how can we make financial accounts accurate?"
Apart from understating prices and the volume of imported goods, changing the origin of imported goods is also used for tax evasion, Mr Apisak said.
For example, companies that import oranges from Spain are subject to 30% import duty as Spain does not have a free-trade agreement with Thailand. They may change the origin of the oranges to China, which has a trade pact, to understate tax bills.
The military-backed government has implemented the single financial account scheme in a bid to attract small and medium-sized enterprises (SMEs) to pay the correct taxes.
Under the scheme, registered SMEs with annual sales of up to 500 million baht are exempt from backdated tax scrutiny. Those with registered capital not exceeding 5 million baht and revenue not exceeding 30 million baht for the 2015 accounting year have no tax burden for the 2016 accounting year.
A 10% corporate tax will be imposed on those with net profits exceeding 300,000 baht for the 2017 accounting year, and a tax exemption will be allowed for net profits of up to 150,000 baht.
SMEs will resume paying normal tax rates from 2018. They are currently exempt from corporate tax for net profits of up to 300,000 baht, but pay 15% tax for net profits of 300,001 to 3 million baht and 20% for net profits of more than 3 million.
Mr Apisak said the Customs Department had tried to stem loopholes used for tax evasion by buying data of worldwide prices for imported goods as a reference, with the data updated every week.
Customs officials weigh containers to determine the volume of imported products but need to tighten scrutiny to prevent importers changing products' origin, Mr Apisak said.
He estimates the government's tax revenue will be raised by 100 billion baht if the single financial account scheme is successful.
If it still faces corruption and tax evasion, it will be difficult for Thailand to escape the middle-income trap to become a high-income country, he said.