The department currently bases its tax mostly on ex-factory prices, except for liquor and beer for which excise tax collection was recently changed and is now based on the last wholesale price before reaching consumers.
Department director-general Somchai Pulsawas argued that the proposed change to a retail price tax base would "increase efficiency" in the collection of the tax.
Basing the tax on the retail price would bring fairness to both domestic and foreign producers, he said. There were problems with importers declaring low import prices, allowing them to pay a low tax and then sell the goods at lower prices than locally made products.
He made no reference to the impact of the change on consumers.
Mr Somchai said the change in the base price for excise tax would not impact the collection of customs duty, which would continue to be based on CIF (cost, insurance and freight) prices so Thailand would not break the agreement with the World Trade Organisation.
"The Customs Department will continue to base its tax on CIF price but the price should be more realistic, while the Excise Tax Department will use a base price of the retail price," he said.
Excise tax is collected from luxury goods, so-called "sin goods", and products that may impact the environment.
However, there is no clear direction on the adjustment of tax rates.
The department has proposed to Finance Ministry its tax reform as ordered by the National Council for Peace and Order. It plans to integrate seven related acts into one law and modernise the law particularly on the collection and base price, as well as penalty clauses.