There is evidence that the US government, in tandem with the Mexican government, is flagging the passports of US citizens who are crossing the border to work on the immigration issue. A couple of weeks ago NBC broke a story about lawyers and journalists either being deported from Mexico at the request of “a foreign government,” or being subjected to extended interrogation at the border. Oregon Senator Ron Wyden is looking into this, and has requested information from the Customs and Border Patrol regarding these events.
Now, here is a first-hand account from a religious leader, a co-founder of the New Sanctuary Movement, who has traveled to Mexico to offer spiritual counseling to migrants. Her passport has been flagged. https://www.buzzfeednews.com/article/kajidousa/opinion-i-prayed-with-migrants-now-the-government-is