Sometimes carrying on with work in the United States can be difficult, especially for Non-Residents. Taxes still should be paid regardless of whether you are a resident. To document taxes as a non-resident, one needs to have an Individual Taxpayer Identification Number (ITIN). As per the IRS website, examples of Individuals who need an ITIN are:

A nonresident outsider individual guaranteeing a tax deal benefit
A nonresident outsider recording a U.S. tax return
A resident outsider (who is treated as a resident outsider for personal tax purposes based on his or her days of presence in the United States) who files a U.S. tax return
A resident or nonresident outsider individual who can be guaranteed as a ward of a U.S. resident or resident outsider on a U.S. tax return
A resident or nonresident outsider spouse who isn't recording a U.S. federal tax return (including a joint return) but who can be guaranteed as a ward on a U.S. tax return
A resident or nonresident outsider choosing for document a joint tax return with a spouse U.S. resident or resident outsider
A nonresident outsider student, professor, or researcher recording a U.S. tax return or guaranteeing an exemption
A resident or nonresident outsider individual who can be guaranteed as a reliant or a spouse of a nonresident outsider U.S. visa holder (https://www.irs.gov/taxtopics/tc857)
To apply for an ITIN, you should record form W-7, Application for IRS Individual Taxpayer Identification Number alongside identity documents that confirm both your identity and your unfamiliar status. Identity documents must be submitted in their unique form or as a guaranteed duplicate from the issuing office.
* Applicants guaranteed as dependents who need to demonstrate U.S. residency must provide extra unique documentation on the off chance that the passport doesn't have a date of section into the United States. See Proof of U.S. residency for applicants who are dependents beneath.
** Might be used to establish unfamiliar status provided that documents are unfamiliar. https://www.irs.gov/instructions/iw7
Form W-7 can be recorded via mail or in person at an IRS Taxpayer Assistance Center (TACs) in the United States by arrangement as it were. When the form has been gotten by the IRS, it will require about 7-10 weeks to process. From that point forward, you will accept your ITIN by means of mail and you can start filling taxes.