You will report the income on Schedule C, but may not deduct any expenses on Schedule C. Self-employment tax (Social Security and Medicare) are reported on Schedule SE. Please see the following excerpt from an IRS online statement on the topic.
"If you are a U.S. citizen working in the United States
for a foreign government or international organization, you must report
this compensation as wages on Form 1040 and pay self-employment tax on
the compensation under the Self-Employment Contributions Act (SECA).
Self-employment tax is computed on Schedule SE, Self-Employment Tax,
and is also reported on Form 1040. Although you are subject to
self-employment tax on this employee compensation, you are not
"self-employed" for any other federal tax purposes. You may not claim
deductions for expenses on Schedule C and are not qualified to establish
a Simplified Employee Pension (SEP) Plan and there is no allowable
deduction for contributions to any such plan. Rules of contributing to
SEP/IRA plans are explained in IRS Publication 560, Retirement Plans for Small Business, and Revenue Ruling 73-384 for additional information."
Source:
https://www.irs.gov/individuals/international-taxpayers/employees-of-a-foreign-government-or-interna...
