"Stop Press" or "Stop the Presses" is a phrase stemming from the printed news media industry as an exclamation signifying the discovery of the need to change the content of an issue just before, or during its printing.
Since this meant that the printing press literally had to be stopped or delayed and much of the existing copies of a publication which had already printed had to be discarded - which carried extreme cost, it is a phrase indicating the arrival of extremely significant news or the discovery of an extremely grave error. The phrase is common in an idiomatic context, referring to the discovery of significant information and is often used sarcastically.
Moss Hart said that he and Irving Berlin did not want to write the typical revue with "blackout sketches" and musical numbers, and they had the idea of doing a topical revue "right off the front pages of the newspapers." Berlin deferred his own fees as composer, lyricist, and theater owner, keeping the cost of the show to a "restrained" $96,000.