Yes, a threat in response to protected activity can constitute retaliation. See Stallard v. Norfolk Southern R.R. Co., ARB No. 16-028, ALJ No. 2014-FRS-149, slip op. at 8-9 (ARB Sept. 29, 2017); Vernace v. Port Auth. Trans-Hudson Corp., ARB No. 12-003, ALJ No. 2010-FRS-018, slip op. at 2 (ARB Dec. 21, 2012).