The Ten Percent Plan required:

10 percent of the 1860 voting population in the rebelling southern states to swear an oath to the Union before that state could be readmitted to the Union.

Explanation:

The 10 percent plan was Lincoln's idea during reconstruction that gave a general pardon to all Southerners except high-ranking Confederate government and military leaders. It required 10 percent of the 1860 voting population in the former rebel (southern) states to take a binding oath of future allegiance to the United States and the emancipation of slaves.