The Federal Aviation Administration has initiated almost 550 investigations into "unruly passenger events" on US airlines so far in 2021. That's more investigations in less than 6 months than in the entire years of 2018, 2019, and 2020 combined. That information is even more shocking when you realize that the level of air travel in 2021 is still far from average.
According to the FAA, 75 percent of the occurrences have apparently been connected to face coverings, with a majority of passengers refusing to wear masks or face coverings. The FAA implemented a strong "zero tolerance" approach at the start of the year, and has so far levied fines totaling more than $680,000 this year.
Source: Federal Aviation Administration (year to date for 2021), chartr