Former Disney Contractor (in 2012) here. I was working for a Disney Contractor in the Disney Offices in Celebration, FL (about 1.5 miles from the Magic Kingdom Gate). I knew of the Disney Contractor rule from Day One, and was reminded of it almost every week. I would have co-contractors leave, to be replaced by another contractor the next month. It was pretty commonplace in our little department.
They did mention that there were ways around Disney's rules, but the 18 Months on, 1 year off rule was something Disney has had for years.
Could be some (inhumane, but not outright evil) reasons for this.
- If you fire all your employees, then a month later have all the same people working for you as contractors, that can (and probably should) be a strong signal to regulators that you are abusing contractor status and ought to be paying for payroll taxes, healthcare, etc.
- Security. If you had just laid someone off, would you hand him root passwords for production infrastructure a week later? Once you've given someone a reason to hurt your company, probably best not to give them the keys back, at least until they've cooled down and found employment elsewhere (this could be the reason for the 1-year waiting period.)
Not an IRS Rule, but it is something bigger companies want to implement so they don't have to pay for benefits for the contractor. When googling it, most I come up with is that most big companies don't want to make it look like they are using temporary work in place of a permanent employ.
They did mention that there were ways around Disney's rules, but the 18 Months on, 1 year off rule was something Disney has had for years.