The "In God We Trust" license plates that have quickly become a fixture on Indiana roads came under a legal attack Monday claiming the law authorizing them is unconstitutional for favoring that message over those on other plates.

The lawsuit filed in Marion Superior Court claims the state Bureau of Motor Vehicles gives preferential treatment to motorists wanting the plates, which also feature the American flag, because they don't have to pay the $15 administrative fee that the agency collects on sales of most other Indiana specialty plates.

The BMV charges the administrative fees in addition to other costs of up to $25 whose proceeds support the causes of the groups or universities promoted by other specialty plates.

The lawsuit filed on behalf of plaintiff Mark E. Studler by the Indiana branch of the American Civil Liberties Union names the BMV and its commissioner, Ron Stiver, as defendants.

"It amounts to a promotion of the plate. The plate is a statement," said ACLU-Indiana attorney Ken Falk. "There is a cost in Indiana to obtain a general specialty plate and to express oneself in that manner, but there is no cost for an 'In God We Trust' plate."

BMV spokesman Greg Cook said he could not comment on pending litigation.

The administrative fees are split among the agency's governing BMV Commission, which receives $9, and road maintenance funds, which receive $6, Cook said.

The 2006 legislation creating the plates specified the state could charge no more for them than the cost of its standard plates.

The legislation's primary author, Rep. Woody Burton, R-Greenwood, noted the BMV has distributed more than 515,000 of the "In God We Trust" plates in less than four months. They became available Jan. 1.

"It seems unfortunate that someone that doesn't like it would keep others from having it," Burton said.

Unlike other license plates that promote ideas or causes such as the Indianapolis Colts, the arts and service groups, the "In God We Trust" plates do not benefit any faith group or other organization, Burton said.

"It is not a special-interest plate," he said. "It is a stock item. It's the motto of the country. It's on the dollar bill."

The complaint said Studler, to express his support for Indiana's environment, pays $40 more than normal registration fees for an "Environment" specialty plate. Of the total fee, $25 goes to a state trust to buy land for conservation and recreational purposes and the remaining $15 goes to administrative costs.

The complaint said "it is not reasonable to charge Mr. Studler administrative fees that are not assessed against persons who purchase the 'In God We Trust' plate."

Falk said Studler was one of more than 10 people who have approached the ACLU with objections to the new license plate including the disparity in fees compared to other specialty plates. They allege that the BMV is encouraging customers to choose the new plates over the other standard plates bearing the state's Web site address, www.in.gov.

"We've received numerous complaints, many of them saying it's violation of separation of church and state, others complaining about the disparity, and about the encouragement," Falk said.

Cook of the BMV said the "In God We Trust" plates cost the agency $3.69 each to produce, compared with $3.19 each for the standard plate with the Web address.

However, since the BMV is replacing the latter with a new standard plate in 2008, the popularity of the "In God We Trust" plate might result in agency savings next year. Customers receiving the "In God We Trust" plates this year will need to receive only renewal stickers the next four years rather than new license plates, Cook said

However, the BMV does not promote the "In God We Trust" plate, which generally are available only through license branches and not through mail-in or Internet renewals, Cook said.

The "In God We Trust" plates currently appear on less than half as many cars as those bearing the standard plates, Cook said. That ratio does not include trucks and recreational vehicles.

Falk said he would not disclose plaintiff Studler's hometown.