A US Work Assignment Under 183 Days: When the Treaty Keeps a Canadian Employee Out of the US Tax System Entirely

Short US assignments live or die on one treaty article. The default rule sources employment income to where the work is performed — a Toronto engineer's eight weeks commissioning a Georgia plant is, by default, US-source income taxable on a 1040-NR with employer withholding obligations attached. Article XV(2) writes the exemption that makes ordinary business travel and short secondments workable, on two alternative branches. Branch one: total remuneration for the US employment in the year is US$10,000 or less — a per-employee, per-year ceiling that quietly covers conference trips and scattered customer visits. Branch two, the assignment branch, with three cumulative conditions: the employee is present in the US for 183 days or fewer in any twelve-month period beginning or ending in the year; the remuneration is not paid by or on behalf of a person who is a resident of the US; and the remuneration is not borne by a permanent establishment the employer has in the US. Satisfy either branch and the US workdays' pay is taxable only by Canada — no 1040-NR, no US withholding, ordinary Canadian payroll throughout. The traps are in the conditions' fine print. The day test counts presence, not workdays, over any rolling twelve months spanning the assignment — a November-to-May secondment straddling two calendar years still aggregates within one window. Paid by or on behalf of a US resident catches secondments where the US affiliate is the economic employer — reimbursement arrangements, cross-charges, and who directs the work all feed an economic-employer analysis; a chargeback of the Canadian's salary to the US entity is the classic condition-killer. Borne by a US permanent establishment does the same where the Canadian employer has a US branch whose books absorb the cost. And the exemption's failure is not partial: outside Article XV(2), the US workdays' pay is taxable from the first dollar, with the compliance stack — federal and state withholding, the employee's 1040-NR, foreign tax credits in Canada — arriving as a set. State tax adds the final asterisk: states are not treaty parties, and while short assignments usually fall under state de minimis practices or simply escape attention, an aggressive state with a long assignment is a separate analysis the treaty does not settle.

Key takeaways

• Branch one: ≤US$10,000 total US-employment remuneration in the year — the traveler's exemption; no other conditions.
• Branch two: ≤183 presence days in any twelve-month window, AND pay not from a US-resident payer (economic employer counts), AND not borne by the employer's US permanent establishment. All three, cumulatively.
• Count presence days across rolling windows: vacation days, weekends in-country, and adjacent personal travel all count; assignments straddling year-end aggregate in the spanning window.
• Chargebacks are the silent killer: intercompany cost allocations pushing the seconded salary onto the US affiliate's books convert the payer condition's answer — assignment structuring is an accounting decision as much as an HR one.
• When the exemption holds: no US federal filing for the employment income, Canadian payroll continues untouched, and the employer's file (assignment letter, day log, cost-bearing documentation) is the evidence that keeps it that way.
• When it fails: US-source pay from day one — employer withholding exposure, the employee's 1040-NR with the workday allocation, Canadian foreign tax credits on the T1, and the state question examined on its own; failing knowingly and structuring for it beats failing retroactively in an audit of the chargeback ledger.

Designing an assignment to pass

The pre-assignment checklist is four lines: project the presence days across every twelve-month window the assignment touches, with buffer; keep the employment contract, direction, and payroll with the Canadian entity; freeze intercompany charging of the assignee's compensation to any US entity or branch for the duration (charge project fees, not the person's salary, where commercial reality allows); and paper it — the assignment letter reciting the structure, the day log, the payroll trail. Where the projections can't pass — a ten-month build, a US economic employer by necessity — the design flips to clean compliance from day one, which costs withholding administration and returns but never penalties.

Worked example

A Waterloo automation firm sends two engineers to a client's South Carolina plant. Engineer one: a 140-day commissioning assignment, employed and paid by Waterloo, the client billed a fixed project fee, no US office or branch — presence under 183 in every window, no US payer, no PE bearing her salary: Article XV(2) exempts her entirely; she files nothing American, her Canadian payroll never blinks, and the firm's file holds her day log and the billing structure. Engineer two: seconded ten months to the firm's own US subsidiary, which reimburses his salary under the intercompany agreement — the day test fails and the payer condition fails independently (the US subsidiary bears the cost): his US workdays are US-taxable from the start, US payroll withholding runs through the subsidiary, South Carolina takes its share, his 1040-NR allocates by workdays, and his T1 claims the credits. Same firm, same client state, one article apart — and the design meeting that sorted each engineer onto the right track happened before either packed, which is the only time it's a choice.

Official sources

"The recipient is present in that other State for a period or periods not exceeding in the aggregate 183 days in any twelve-month period commencing or ending in the fiscal year concerned, and the remuneration is not paid by, or on behalf of, a person who is a resident of that other State and is not borne by a permanent establishment in that other State." — Canada-United States Tax Convention, Article XV(2) (as amended by the 2007 Protocol), https://www.canada.ca/en/department-finance/programs/tax-policy/tax-treaties/country/united-states-america-protocol-2007.html

"FDAP income is taxed at a flat 30 percent (or lower treaty rate, if qualify) and no deductions are allowed against such income. ... Effectively Connected Income, after allowable deductions, is taxed at graduated rates." — Internal Revenue Service, Taxation of Nonresident Aliens, https://www.irs.gov/individuals/international-taxpayers/taxation-of-nonresident-aliens

Practitioner note

Article XV(2) is the workhorse of cross-border staffing and it fails on accounting, not travel: the chargeback nobody told the tax team about undoes more exemptions than any day count. Our assignment protocol is the four-line checklist — windows projected, Canadian employment intact, salary charges frozen, file papered — and where the facts can't pass, we say so before departure, because a planned compliance stack is routine and a reconstructed one is a penalty conversation.

See also: Browse every cross-border tax topic guide, organized by situation.

Next step

Fairlight prepares the assignment design review — Article XV branch testing, rolling-window day projections, intercompany charging structure, the evidence file, and full-compliance setup where the exemption can't hold. See cross-border pricing or book a call.