A fascinating website called the Jewish-American History Foundation has a remarkable letter a father wrote to President Abraham Lincoln, enjoining him to allow his son, then a Jewish soldier in the US Army, to observe Shabbat.
To His Excellency Abraham Lincoln, the President of the United States.
By your order of the 16th day of November, 1862, you recommend that the officers and men of the army shall observe the Sabbath and do no work on Sunday, because we are a Christian people. But according to the Declaration of Independence and according to the constitution of the United States, the people of the United States is not a Christian people, but a free, sovereign people with equal rights, and each and every citizen of the United States has the right and liberty to live according to his own consciousness in religious matters, and no one religious denomination, be it a majority or minority of the people, can have a privilege before the other under this our beloved constitution.
Now by the order of your Excellency you give the privilege to those officers and men in the army who by their religious creed do observe the Sunday as a holy day and a day of rest; but you make no provision for those officers and men in the army who do not want to observe the Sunday as a holy day, (as for instance those Christians called the Seventh-day Baptists and the Jews, who observe the Saturday as a hold day and a day of rest,) that they may enjoy the same privilege as those who observe the Sunday as a holy day, as well as for the heathen or the so called infidels, who do not want to celebrate either the Sunday or the Saturday as a Sabbath, but choose perhaps some other day as a day of rest.
Now I stand before you as your namesake Abraham stood before G-d Almighty in days of yore, and asked, "Shall not the Judge of all earth do justice?" so I ask your Excellency, the first man and President of all the United States, Shall you not do justice? shall you not give the same privilege to a minority of the army that you give to the majority of it? I beseech you to make provision, and to proclaim in another order, that also all those in the army who celebrate another day as the Sunday may be allowed to celebrate that day which they think is the right day according to their own conscience; and this will be exactly lawful, as the Constitution of the United States ordains it, and at the same time it will be exactly according to the teaching of the Bible, as recorded in Leviticus xix. 18: "Thou shalt love thy neighbor as thyself."
I gave my consent to my son, who was yet a minor, that he should enlist in the United States army; I thought it was his duty, and I gave him my advice to fulfill his duty as a good citizen, and he has done so. At the same time I taught him also to observe the Sabbath on Saturday, when it would not hinder him from fulfilling his duty in the army. Now I do not want that he shall be dragged either to the stake or the church to observe the Sunday as a Sabbath. Your Excellency will observe in this my writing that I am not very well versed in the English language, and if there should be found a word which is not right, pardon it, and never such a word shall be construed so as if I would offend your Excellency or the people; for I love my country, the Constitution, and the Union, and I try to be always a loyal citizen.
I remain, respectfully, your most obedient servant and fellow citizen,
Narrowsburg, Sullivan Co. N.Y. Dec. 4, 1862
The letter above, asking Lincoln to allow his son (and other Jewish soldiers) to observe Shabbat, was written by Bernhard Behrend, then of Narrowsburg, NY, on behalf of his son, Adajah Behrend (1841-1932) a hospital steward and field officer, who went on to practice medicine in Washington DC.
We often hear how keeping Shabbat was a great struggle for European Jewish immigrants at the end of the 19th century and the early 20th century, and here we see that there were certainly early challenges to Shabbat observance in the US.
I was also struck by Bernhard Behrend's apologies for his English skills, when I found his writing to be quite eloquent.