I think if you deduct business expenses, you are claiming that you are self employed. Not quite sure about that though.

Self-employed means you owe 15% self-employment tax.

The IRS audited a bunch of expat pilots this past two years including me. One of things they said I owed was self-employment tax, plus penalties and interest. There is a description in one of the IRS forms on what is, and is not, a self-employed contractor vs an employee. I printed it out, highlighted the section, and sent it to them with all my credentials from my foreign jobs, and the proof that I met the criteria of an employee.

They accepted it, and I won.