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If you're looking for a book, it looks like Act of Justice: Lincoln's Emancipation Proclamation and the Law of War by Burrus M. Carnahan covers the topic.

The proclamation is sometimes called Jessup's Proclamation after Thomas Jessup who Jackson put in charge of the Seminole War. I can only find scraps about it on line.

It was a complicated situation, because not only were some Seminoles slaveowners, but many were part-African and feared being enslaved by US plantations if they lost the war.

[BroJoeK]

"The proclamation is sometimes called Jessup's Proclamation after Thomas Jessup who Jackson put in charge of the Seminole War.
I can only find scraps about it on line."

Found it! Jessup's Proclamation

"Documented History has proven that this was the “1st Emancipation Proclamation”.

Jesup’s Proclamation.

“Jesup’s Proclamation,” as it came to be known, pre-dated Lincoln’s by twenty-five years, yet both acts shared a legal origin in the arguments of John Quincy Adams.
It was Adams who, in 1836, first asserted that the U.S. Army could liberate rebellious slaves in time of war:

“By war the slave may emancipate himself; it may become necessary for the master to recognize his emancipation by a treaty of peace.”

Within two years of Adams’ speech, his arguments found their first practical application when General Jesup offered freedom to rebellious Black Seminoles in Florida.
Jesup made the offer for military reasons, to separate the blacks from the Indians; this move, he wrote the Secretary of War, would “weaken [the Indians] more than the loss of the same number of their own people.”

Significantly, “Jesup’s proclamation,” as the Black Seminoles came to call it, was the first emancipation of rebellious blacks in U.S. history.*
And it was implicitly premised upon federal authority under the war powers."

John Quincy Adams befriended young Illinois Congressman Abraham Lincoln, who doubtless listened attentively to Adams' legal theories.