A family member of mine used to process and route various things at the IRS for 3 or more years; I won’t say which one.
One of the things that they did was route mailed-in letters and other items where people “told” on others. They told me three things about it.
They get a LOT of reports that come in with almost no hard information, wild speculation, or facts that are just plain wrong. Some reports are along the lines of “my neighbor who drives a blue Cadillac (no tag number) and who lives in this State hasn’t paid taxes for a long time, or so they told me once. Please do something about it KTHXBYE.” Or even better, some are as crazy as “a lot of people in this city don’t pay taxes; please do something about it.” For each letter like that which arrives, they still[ have to do something about it. They have to at a minimum write a report about receiving the report, and then explain why they chose not to do anything about it. This seems simple, but I was told it takes a lot of effort.
Anonymous reports, even ones which have lots of detailed information with them, are not taken nearly as seriously as non-anonymous ones. However, something like a sworn affidavit which has hard, factual information attached gets jumped on at once, and (reputedly) those can get jumped on the same day they’re received. Why? Because they represent the “low hanging fruit”, and investigators need to have some successes under their belt.
They never heard of anyone becoming a “target” by the IRS by telling on another person. What they did hear of was people becoming inadvertent targets, such as a person who complained that their boss was dodging taxes, and when they were following the money trail they discovered the boss gave out cash bonuses that weren’t claimed on taxes by many folks, including, presumably, the employee who told on the boss. Which reminds me of a time I know of when a person reported their boss for having illegal software on their PC at work, which resulted in a Department-wide PC audit, which ended up, surprise, finding illegal software on the person who did the reporting.
They never said anything about a $2M priority limit, but it seems reasonable, given that there are a very limited number of investigators with very limited time.