Most poor people don't work at all, and about half of those who do are only part time.

If by "most" you mean ~10% (or were you including children and old people?)

I can't find any solid statistics, but there is certainly evidence for a 'significant number': http://poverty.ucdavis.edu/policy-brief/low-wage-work-uncert...

I wasn't specifically thinking about people below the poverty line, but was rather intending to include the "working-class" as well.