Employees may claim exemption from withholding if one of the following conditions apply:
Residents of Canada and Mexico performing in transportation service between the US and Canada or Mexico.
Residents of Canada and Mexico perform duties connected to the construction, maintenance , or operation of a water-way, viaduct, dam, or bridge crossed by, or crossing, the boundary between the US and Canada or the boundary between the US and Mexico.
Nonresident aliens that are residents of the US Virgin Islands are not subject to withholding tax on income earned while temporarily employed in the United States.
You must send a copy of this form, if:
The employee claims more than 10 withholding allowances.
The employee claims exemption from withholding and the employee's wages would normally exceed $200 per week.