Fight with terrorists, lose your passport.
Sen. Ted Cruz (R-TX) introduced the Expatriate Terrorists Act, S.2779. It's pretty simple. If you are US citizen and you fight with terrorists you lose your US passport. It amends Section 349(a) of the Immigration and Nationality Act.
The ACLU Urges Opposition to S. 2779, Expatriate Terrorists Act and considers it unnecessary and dangerous. The companion Bill is H.R. 5450.