Worrell, Davidson, and Sharma (1991)
Worrell, Dan L., Wallace N. Davidson, and Varinden M. Sharma, "Layoff Announcements and Stockholder Wealth." Academy of Management Journal, 38(3), 1991.
From authors' abstract: "We tested the reaction of the securities' market to announcements of 194 layoffs. Investors reacted negatively to announcements attributable to financial reasons. Negative preannouncement reactions occurred when negative hints about firms preceded announcements, and announcements of large or permanent layoffs elicited stronger negative responses than other announcements."