This is a complex area of employment law and you can never read too much about it. The Oregon Law Practice Management blog has this 12/3/12 post:
Excerpt: ‘For those of you who like to use “independent contractors” (contract lawyers, contract paralegals, freelance legal secretaries) take heed. Your contractor may well be an employee.
The latest case to interpret ORS 670.600 is Compressed Pattern, LLC v. Employment Department Tax Section.
In Oregon, an independent contractor must be “customarily engaged in an independently established business.”….’ [Link to full blog post.]