Well, this isn't squarely military justice, but it involves military lawyers (judge advocates, or JAGs) who are an integral component of military justice: see here for the flawed proposal by the Trump Admin to federalize National Guard JAGS to ... wait for it ... serve as Article I immigration judges.
OK, these so-called civilian "judges" (actually, employees of the executive branch, as they serve the Attorney General) on their best day are not independent nor impartial, but they claim to be. Importantly, any federalized military lawyers serving in such quasi-judicial (but really, law enforcement role) -- if the President doesn't invoke the Insurrection Act (no facts support such invocation) and if he doesn't find another (non-existent!!) express statutory exception to the Posse Comitatus Act (PCA), such use of these military JAGS is unlawful. Recall that the PCA prohibits active duty and federalized military members from executing the law, that is, serving in law enforcement roles, unless there is an express statutory or constitutional exception. The reason behind the PCA is that we Americans don't like living under domestic military occupation and don't want to be ... that is, we don't want to live under martial law nor come close. And guess what? Per our Supreme Court, military tribunals (military courts) hearing civilian cases -- prosecuting or otherwise deciding the legal fate of civilians -- are the hallmark of martial law in the US. And doesn't a civilian immigration court, if headed by a MILITARY JUDGE, sure look like a military tribunal?
As a resident of Los Angeles, I've witnessed firsthand the increasing militarization of immigration enforcement in the US. Recall Martin Niemoller's powerful WWII warning: "First they came for the socialists, and I did not speak out—because I was not a socialist. Then they came for the trade unionists, and I did not speak out—because I was not a trade unionist. Then they came for the Jews, and I did not speak out—because I was not a Jew. Then they came for me—and there was no one left to speak for me."