'Toe the line' may have a nautical origin.

Earliest quote in the OED from Maryat, a marine novelist, 1833- "He desired us to toe a line..."
R. H. Dana, 1840, "Two Years Before the Mast" - "The chief mate...marked a line on the deck, brought the two boys up to it, making them 'toe the mark'."
Westm. Gaz., 1895, The phrase 'Toeing the Line' is very much in favour with some Liberals..."
1853- 'Toeing the scratch' for business.