NEW YORK (CNNMoney.com) -- Three Republican senators have written to Attorney General Alberto R. Gonzales questioning Boeing's settlement with the Department of Justice that may allow the plane maker to write off the $615 million fine as a tax deduction, according to The New York Times.

Senators Charles Grassley (R-IA), John McCain (R-AZ), and John Warner (R-VA) wrote that allowing Boeing to deduct payments to the government "would be unacceptable."

Boeing was ordered to pay the penalties in order to avoid criminal charges related to the improper hiring of a Pentagon official and the theft of data from Lockheed Martin Corporation, the newspaper reported.

Fines corporations pay to the government to settle charges are not tax deductible, although the parts of the settlement considered compensatory can be.

"If Boeing is able to deduct the settlement, the real penalty could be millions and millions less than advertised. If the Justice Department failed to take into account the tax implications of the $615 million settlement, that's inexcusable," Sen. Grassley said in a statement.

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