AUBURN, Wash. -- The Sounder commuter train is booming with business, but riders say they're frustrated by the lack of accessible parking spots. At times they've had to give up the train and just drive to work.

Sounder commuters in Auburn are especially upset because of some parking slots that sit empty.

The Sounder commuter train pulls into the Auburn station right on time for the morning run to Seattle. The folks climbing on board consider themselves lucky. They were able to find parking.

"It was always bad, but there was never any parking for the last train anyway and now it's gotten even worse," said commuter Jeff Cunningham.

The six-story parking garage is filled to capacity; there's no more room.

What really angers commuters is that when they come around the corner, they see empty slots, but they can't park here. It's all because of ADA. That's not the Americans with Disabilities Act. It's the Auburn Downtown Association.

Forty three parking spaces are reserved by the city of Auburn, though you can buy a permit to park in one of the spots for $100 a month.

"That's pretty pricey. It'd almost be more worthwhile to park in Seattle," said Seth Barry, a commuter.

When told the commuters see the fee as blackmail, Auburn Mayor Pete Lewis responded, "well, let's go back and take it a couple of steps at a time."

Lewis says commuters shouldn't blame the city.

Auburn paid to build part of the garage in trade for 180 parking stalls for downtown shoppers. But they've given back all but 43 to Sounder commuters.

"We're not even using a majority of the slots that we could, most of which we've tried to give back for the commuters. Some were kept for business," Lewis said.

Lewis says his office has heard from a lot of upset commuters.

"I appreciate that and my suggestion would be to keep calling and e-mailing and writing to Sound Transit and ask them when will the second parking garage be built," he said.

"We understand and are sympathetic that parking is a major issue in the south corridor. It's an extremely popular service," said Bruce Gray of Sound Transit.

Sound Transit says voters hold the key.

"We would like to build more parking in Auburn. We don't have the money to do it today and to do that, we need voter approval," said Gray.

Look to see a transit measure on the ballot, possibly as early is this November.

Auburn's mayor warns that parking is only going to get more challenging later this year when two more trains are added to southern route.