Who would oppose this decision? Why might they do so?

What i said was that most Southerners would oppose this decision because they own large plantations and farmers and/or wealthy people/families don't and/or do the work by themselves.
However, I wasn't so sure about my answer.

The South's economy depended upon slaves to do the tremendous amount of backbreaking labor. The plantation owners believed they couldn't make a profit if they had to pay laborers to do this work.