Per the instructions for Form 5329, on page 4, distributions from a SIMPLE IRA may result in a 25% additional tax instead of the additional 10% tax imposed on an early withdrawal of other IRAs:

Line 4

If any amount on line 3 was a distribution from a SIMPLE IRA received within 2 years from the date you first participated in the SIMPLE IRA plan, you must multiply that amount by 25% instead of 10%. These distributions are included in boxes 1 and 2a of Form 1099-R and are designated with code S in box 7.

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