Some passengers on a SkyWest Airlines flight from Los Angeles International Airport to Denver were not wearing face masks after the federal mask mandate ended.

Patrick T. Fallon/AFP via Getty Images

The judge relied on her interpretation of the term "sanitation" when tossing out the transportation mask mandate.

The Public Health Service Act of 1944 gave the federal government the power to respond to public health emergencies.

The Public Health Service Act was used by the Biden administration to defend the COVID-19 mask mandate.

The law says that if the government is trying to prevent the spread of communicable diseases, it can provide for such inspection, extermination, disinfection, Sanitation, pest destruction of animals or articles found to be so contaminated as to be sources of dangerous infections.

Under the law, the administration argued that masks qualified as "sanitation", but Mizelle chose to exclude face coverings from the definition. Legal experts say her interpretation was off.

"If one of my students turned in this opinion as their final exam, I don't know if I would agree that they had gotten the analysis correct."

She said that it reads like someone who decided the case and then tried to dress it up as legal reasoning without actually doing the legal reasoning.

What counts as 'sanitation'?

According to her opinion, a common way judges decide the meaning of words in laws is to look up dictionary definitions that were written before the law was enacted. That is 1944 in this instance.

It could have been taken to mean either actively cleaning something or measures to keep something clean, but ultimately settles on the former definition.

A mask doesn't clean anything. The person wearing the mask doesn'tsanitizes the conveyances.

There are other words listed alongside "sanitation" in the 1944 law, such as "fumigation" or "pest extermination".

The term "sanitation" is not used in the public health field or understood by the U.S. Centers for Disease Control and Prevention, according to Fuse Brown.

She said thatitation was just the old way in public health parlance of taking traditional public health steps to prevent the spread of disease.

The Public Health Service Act came about two and a half decades before the widespread mask-wearing during the 1918 flu outbreak.

She thinks the opinion will make it harder for the Biden administration to control the spread of COVID-19.

The reasoning is poor, but it also has dire consequences for public health, which is the part that makes it not just a joke, but it actually makes it really frightening.

The opinion could have lasting effects on the CDC's authority

Legal experts warn that if the opinion is upheld by a federal appeals court or the U.S. Supreme Court, it could hurt the government.

If this particular type of opinion took on greater precedential value as it rises up through the court system, it would be a big problem for the CDC.

She replaced her definition of "sanitation" with her own, brushing aside a legal norm known as "agency deference" that requires judges to yield to the interpretation of federal agencies when a law's language is unclear.

The agency did not follow standard rulemaking procedures before instituting the mandate. During a national public health emergency, the federal government operates differently.

This is a serious deviation from what we are trying to do to protect the public's health, but a misstatement of federal authority in emergencies to a great degree.

The opinion amounted to a "breathtaking amount of political judicial activism" that should chill us all, according to Fuse Brown.

Even if we are skeptical about agencies or Congress, we do not want these decisions to be in the hands of a single unelected judge.

Pien Huang is a reporter for NPR.