Assignees paid correctly, taxed deliberately.

No, and this is the most common mistake. Article 18-2(2) of the Restriction of Special Taxation Act lets a foreign employee elect to have Korean income tax computed at 19% of employment income instead of the progressive rates. But paragraph (3) is the trade: where the election is made, exemptions, deductions, reductions, and tax credits under the Income Tax Act and the Restriction of Special Taxation Act do not apply, and the income is not aggregated into global income. For an assignee with substantial deductible items or lower compensation, the progressive computation can produce a smaller liability. It should be calculated both ways, per person, per year.

Two separate limits. The election is available for employment income received up to the tax period ending within 20 years from the date the employee first provided work in Korea. Separately, the employee must have first started providing work in Korea on or before 31 December 2026 to fall within the provision as currently enacted. That second condition matters for assignment planning now — an assignee whose Korean start slips into 2027 is on a different footing from one who starts before year end.

This is the question that has actually been litigated. The starting point is "the date work was first provided in Korea," and how that applies to an employee with a break in Korean service has been disputed between the tax authority and the Tax Tribunal — the published position changed over time before being settled by a Ministry of Economy and Finance ruling in 2022. There is a body of Tax Tribunal decisions and NTS interpretations on the point. For a returning assignee, the start date should be established before payroll is set up, not assumed.

It can be applied at both. Under paragraph (4), the withholding agent may withhold 19% when paying monthly employment income, rather than waiting for the year-end settlement. Either way, the employee has to apply for the special case under paragraph (5) — it is not applied by default.