In Tennessee, people who are convicted of DUI after a blood or breath test are required to pay the Tennessee Bureau of Investigations, which performs those tests, a $250 fee. People who are not convicted are not required to pay the fee. The state’s Court of Criminal Appeals recently found that to be unconstitutional because it sets up an apparent conflict of interest and calls the trustworthiness of the test results into question.

Over 20 DUI defendants appealed their convictions, claiming that the testing fees give the TBI an incentive to produce positive test results. They made clear that they weren’t accusing the TBI of actually falsifying any results. Rather, they claimed it “created the appearance of impropriety and the potential for abuse based upon financial interest.” That, they said, violates defendants’ due process rights.

Lawmakers first put a $100 fee in place in 2005, and then raised it to $250 in 2010 at the TBI’s urging. Today, the fees bring in over $3 million each year.

In 2014, the director of the TBI argued that the fees were crucial to their operations. If the fee had not been raised in 2010, he said — and assuming the state did not provide alternative funding sources — the TBI would have had to eliminate forensic scientist positions or charge local law enforcement for the cost of testing. Again, assuming the state didn’t provide any funding, local departments could not afford to pay that cost.

The current fee regime, however, comes at the cost of the TBI’s reputation as a neutral provider of valid test results.

As the Court of Criminal Appeals noted, “under the scenario suggested by the State, the defendant is forced to obtain an independent test, to pay for an attorney to defend him, and to hire an expensive expert to challenge the … result in order to do what an unbiased TBI forensic scientist should have done from the beginning.”

The court ruled that lower courts had been in error when they failed to exclude the test results from evidence. That is, potentially, a wide-ranging ruling. If the TBI’s test results should be excluded from evidence, many past DUI convictions could be reopened or appealed for lack of sufficient evidence.

It is not yet clear whether prosecutors will appeal the case to the Tennessee Supreme Court.