Out-of-state senior citizens won't get the same discount as New Jersey seniors when New Jersey Turnpike and Garden State Parkway tolls increase, unless they get a New Jersey-issued E-ZPass transponder.

And some lawyers say that may illegally discriminate against drivers from Pennsylvania, New York and other states.

New Jersey officials this month approved a plan to give 10 percent off-peak discounts to senior citizens and drivers of "green" vehicles on the two toll roads when general toll increases take effect in early December. To get the discounts, drivers need to use an electronic transponder issued by New Jersey E-ZPass.

That requirement could raise legal questions about fairness under the Constitution's interstate commerce clause, said lawyer Matthew Pawa.

Pawa earlier this month filed a federal class-action lawsuit against the Massachusetts Turnpike Authority for not giving the same discounts to E-ZPass users as it does to users of its own electronic "Fast Lane" program. He is seeking refunds for all E-ZPass users who used the Boston-area toll gates.

"Our theory would prohibit any state transportation agency from discriminating solely on the basis of the state agency issuing the transponder," Pawa said.

In his lawsuit, Pawa argues that "interstate regulatory gridlock would occur if every state adopted a program similar to MTA's Fast Lane Discount Program. In such a situation, a traveler would be required to own 50 different transponders and use them accordingly to secure the benefit conferred under each electronic toll collection system."

Ari Afilalo, a law professor at Rutgers-Camden Law School, said courts might rule either way on the New Jersey discounts.

On one hand, he said, "Why should you discriminate? The old guy from Philadelphia is no different from the old guy from New Jersey." On the other, he said, New Jersey "is not trying to be protectionist, it's just trying to help its senior citizens."

The Delaware River Port Authority last month instituted a similar E-ZPass requirement for a senior discount on its four Philadelphia-area bridges, angering Pennsylvania seniors who don't have New Jersey E-ZPass devices.

On the Turnpike and the Parkway, "the discount for seniors is open to anyone who has a New Jersey E-ZPass account and can demonstrate that they meet the senior criteria," said Joe Orlando, a spokesman for the Turnpike Authority. "We have account holders in all 50 states. We do urge people to enroll in the E-ZPass system that best meets their needs in terms of discounts and service."

No arrangements have been made yet for seniors to apply for the new discounts. Orlando said that information will be available around Nov. 1.

Seniors who get the DRPA E-ZPass discount will also get the discount on the Turnpike and Parkway, Orlando said.

All E-ZPass users will continue to receive a 25 percent discount during off-peak hours (peak hours are 4:30 p.m. to 6:30 p.m. and 7 a.m. to 9 a.m., Monday through Friday, and all Saturday and Sunday).

The AAA auto clubs of New Jersey support the senior-citizen and green-vehicle discounts (for cars that meet standards for low emissions and high gas mileage), said David Weinstein, spokesman for the auto clubs.

"It's an appropriate benefit in both cases. It's not unprecedented, and it encourages greater use of the system," Weinstein said. "We'll see if it stands up to the interstate commerce test."

The interstate commerce argument was rejected by a U.S. Appeals Court in 2003, in a case similar to one brought this month by Pawa. That 2003 ruling upheld a lower-court ruling that the Massachusetts "Fast Lane" discount program "did not discriminate against out-of-state residents and did not excessively burden interstate commerce."

If New Jersey wanted to offer the same senior-citizen and "green" vehicle discounts to drivers with non-Jersey E-ZPasses, it would require changes to the E-ZPass computer software in New Jersey and in other affected states.

The technical changes could be made, but New Jersey officials would have to make policy decisions to do so, said Carrie Hyun, director of corporate communications for Affiliated Computer Services, the Dallas-based company that operates electronic toll collection for New Jersey E-ZPass.

James Crawford, executive director of the E-ZPass Interagency Group, a consortium of transportation agencies offering E-ZPass in 15 states, said granting a discount more broadly "would involve costs that the other [states'] agencies would have to incur."

Crawford said several states offer discounts to their E-ZPass users that are unavailable to all E-ZPass users, including New York, Maryland, Virginia and Maine.

Indiana and Illinois last year squared off over toll discounts. Indiana announced a plan to offer toll discounts only to users of the Indiana system, I-Zoom, and to deny discounts to other electronic system users, including the Illinois system, I-Pass.

After Illinois threatened to retaliate by denying its toll discounts to Indiana users, Indiana relented and agreed to give the discounts to users of all systems.

The costs to New Jersey or other states for establishing broader discounts have not been estimated. Another issue for New Jersey could be the loss of revenue, if discounts were offered to all senior citizens.

The anticipated cost of the new discounts is $12.8 million a year, which would be generated by cutting turnpike jobs and freezing hiring. If those discounts were extended to out-of-state E-ZPass users, the costs would be greater.

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.