"Scathing letter" refers to a strongly critical or harshly worded letter.
Sentences with «scathing letter»
In scathing letters, Park District and school officials argued back and forth about how to deal with flooding. (articles.chicagotribune.com)
A scathing letter sent recently to the director of the personnel management office has alleged, for example, that the compromise is even more extensive than previously thought. (fortune.com)