The letter, signed by five commissioners, said it was clear that a Feb 2 election could lead to several problems.
It warned that the new House of Representatives may not be able to convene after the election because it was unlikely there would be 95% of the 500 MPs present, as required by the charter.
Holding an election under the current conditions could lead to a huge waste of state funds, while the government has the authority to postpone the election by issuing a royal decree to set a new date for the polls, the letter added.
The Office of the Auditor-General on Thursday requested the EC review plans for the Feb 2 election, saying the polls were highly likely to be a waste of public money.
The request was made in an urgent letter to EC chairman Supachai Somcharoen.
In the letter, the Office of the Auditor-General expressed concern over the use of 3.8 billion baht of state funds to hold the election, and the potential cost to voters, both inside the country and abroad, who will use their own money to travel to polling units.
The letter suggested the EC think again about the Feb 2 election, to ensure the best use is made of state funding.