As you know, transgender and other minority employees are as valuable and productive additions to your workforce. Anti-transgender activist groups such as Cathy Brennan may contact you and attempt to intimidate and manipulate you in an effort to threaten your employee's job security.
It is important to note that if one of these groups attempt to contact you, it does not mean your employee has done anything wrong; but rather that they are a target of discrimination.
Here are some resources to further educate yourself to the existence of anti-trans hate groups such as Cathy Brennan's own Gender Identity Watch
Thousands of people have petitioned to properly label Gender Identity Watch as a hate group
To groups such as Gender Identity Watch and other trans discrimination groups, no target is off limits - including 16-year old children
Information regarding Cathy Brennan from RationalWiki