Getting Mac to ask for disk encryption password
The proper tool to add or remove FileVault users is fdesetup.

Open Terminal and enter sudo fdesetup list -extended to get a synopsis.

To remove a user by UUID or user name use:

sudo fdesetup remove -uuid &lt;UUID&gt;
sudo fdesetup remove -user &lt;username&gt;


All users removed won't be able to log-in with their passwords at the first password prompt because they aren't listed anymore. The user still exists as OS user though. To login as such a user either has to use fast user switching or log out as FileVault enabled user and log in with the non-FileVault-enabled user.

To reenable FileVault disabled users either use sudo fdesetup add -usertoadd &lt;username&gt; or open System Preferences > Security > FileVault > hit the "Enable Users..." button and enable a listed user.