The National Immigration Law Center has prepared downloadable "Know Your Rights" documents that your immigrant employees should carry with them in case they are visited by immigration agents:
Espanol: https://www.nilc.org/wp-content/uploads/2016/11/Rights-No-Matter-Who-Is-Pres-esp-2016-11-10.pdf
English: https://www.nilc.org/wp-content/uploads/2016/11/Rights-No-Matter-Who-Is-Pres-2016-11-10.pdf