We all know this year's car-tab fees for drivers in King, Pierce, and Snohomish counties have been costly. But could they also be unconstitutional? Two state senators say yes, and they're asking the attorney general to weigh in.

A letter sent to Attorney General Bob Ferguson's office on Friday outlines the concerns shared by Senator Steve O'Ban and Senator Dino Rossi. The letter also asks Ferguson to weigh in.

"Sound Transit is relying on a repealed provision from 1996 to calculate the Motor Vehicle Excise Tax for ST3," said Senator O'Ban.

The letter explains:

"It has come to our attention that the act which authorized Sound Transit to use the inflated MSRP schedule was improperly drafted in such a way as to violate the state constitution. If so, it is our belief that the invalidation of this provision or act would have legal consequences for any contacts entered into between Sound Transit and any other entity that pledged the MVET (motor vehicle excise tax) revenue. These could include voiding or reforming loans or bond contracts. Because we are considering legislation or other action to address this matter, we are asking your office to provide an informal opinion on this matter."

Rossi and O'Ban cite Senate Bill 5987, the revenue bill for the transportation package that was passed by the legislature in 2015. They say the bill purported to modify the previously existing vehicle valuation schedule, but referenced the general chapter of law in which the provision appears rather than the provision itself -- which is a requirement of the state constitution.

Senator O'Ban said it's complicated, but significant.

"It's really important so that legislators can understand what it is they are enacting," he said. "The constitution requires that you set forth specifically each section that the bill plans to amend or reference. You can't just simply reference a chapter heading. And why that was critical here is because the chapter heading that this bill referenced contained the schedule, the MVET schedule for ST2. ST2's schedule was the one that was based on the vehicle's age, the more reasonable calculation."

O'ban and Rossi feel that both legislators and taxpayers were misled.

"The bottom line in the end is is looks like a very disingenuous effort, and on top of that, people are starting to get their car tab bills and are starting to feel the pain," said Senator Dino Rossi. "I'm here to protect the taxpayers and the people I represent, and that's exactly why we've come forward with this."

He says the information they've learned in recent days shows that Sound Transit should not be using vehicle MSRP to calculate car-tab taxes.

There's been a public outcry over the formula Sound Transit uses to determine a driver's car-tab fees under ST3, because it uses the Manufacturer's Suggested Retail Price (MSRP) to calculate your car's taxable value. It's not at all based on fair market value.

Since the senators are considering legislation to address the issue, they've asked Attorney General Bob Ferguson to provide an informal opinion on the matter.

KING 5 reached out to the Attorney General's office, who confirmed they have received the letter from O'Ban and Rossi. A spokesperson said the letter is now being reviewed by attorneys in the office, but pointed out that the senators themselves acknowledged that the AG's Office does not typically issue advisory opinions on the constitutionality of laws.

The final paragraph of the senators' letter to the AG's Office reads as follows:

"We realize that your office ordinarily does not issue advisory opinions as the constitutionality of laws, however in light of the importance of this matter, we are requesting that your office use whatever means it has, including the employment of outside counsel in addressing potential conflicts of interest."

The Washington State Office of the Attorney General's website defines an Attorney General Opinion as a statement of the Attorney General's official views on a legal question relating to a public officer's duties. I

The AG's Office says an Attorney General Opinion is not typically not appropriate when it comes to questions about the validity of a current state statute or asking whether the state would face liability under a current statute.

But it's important to note, Rossi and O'Ban are seeking an informal opinion.

As for Sound Transit: a spokesperson told KING 5 they were not even aware of the letter sent to the AG's Office, until members of the media started calling. He said they are now reviewing the letter, but couldn't comment further at this time.