> ## Documentation Index
> Fetch the complete documentation index at: https://docs.symmetry.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Lock-in letters in the SPF API

> Use the lockInLetters element to restrict which state and federal withholding forms an employee can change.

At times, the Internal Revenue Service (IRS) may give an employer an order to withhold taxes at a minimum rate. Therefore, SPF API provides a mechanism to prevent employees from changing certain state or federal withholding forms.

## Sample Request

In the sample request below, use the `lockInLetters` element to provide a single state abbreviation or a comma-separated list of states.  For a Federal lock-in letter, use the value `FEDERAL`.

```json theme={null}
{
    "homeAddress": {
        "streetAddress1": "11 S Union St",
        "city": "Montgomery",
        "state": "AL",
        "zipCode": "36130"
    },
    "workAddresses": [
        {
            "streetAddress1": "64 N Union St",
            "city": "Montgomery",
            "state": "AL",
            "zipCode": "36130"
        }
    ],
    "lockInLetters": [ 
     "FEDERAL",
      "AL"
    ]
}
```

<Info>
  **Lock in Letters does not impact Canadian forms**

  The concept of Lock in Letters is only used within SPF United States and is not used within the Canadian implementation of SPF.
</Info>

## Demo

<iframe src="https://player.vimeo.com/video/851348514?badge=0&autopause=0&player_id=0&app_id=58479" title="SPF API: lockInLetters" width="100%" height="400" style={{ border: 0, width: "100%", aspectRatio: "16 / 9" }} allowFullScreen />