Oops my mistake - it does work! :) I had a bit of old data hanging around in my database that led me to believe otherwise.

In the code above*:

    $this->addFieldMapping('field_voices', 1)
         ->sourceMigration('Voices')
         ->arguments(array('source_type' => 'tid'));

The sourceMigration method is referring to the machine name of a term mapping that would have been defined in the hook_register_migrations. This took me some time to figure out.

So, my hook is defined as

/**
 * Register all D6->D7 migrations.
 */
function vsc_migrate_627_register_migrations() {
  // Specify the DB connection and the source Drupal version.
  $common_arguments = array(
    'source_connection' => 'legacy',
    'source_version' => 6,
  );

  // Register migrations.
  _vsc_migrate_627_coupon($common_arguments);
  _vsc_migrate_627_coupon_conditions_terms($common_arguments);
}

The _vsc_migrate_627_coupon_conditions_terms is defined as:

/**
 * @param $common_arguments
 */
function _vsc_migrate_627_coupon_conditions_terms($common_arguments) {

  $args = $common_arguments + array(
      'description' => 'Migrate coupon tags',
      'machine_name' => 'CouponConditionsMigration',
      'source_vocabulary' => $vid = 1,
      // The Vocab Id of the tags on the D6 instance.
      'destination_vocabulary' => 'conditions',
    );

  // We can use the same class as the *Node* terms.
  Migration::registerMigration($migration_class = "VSCTerm6Migration", $args['machine_name'], $args);
}

So, you see where the machine name is defined ... right?
Then in my class VSCCoupon6Migration extends DrupalNode6Migration, we map it using:

    /**
     * Taxonomy Terms.
     *
     * This leans on the Classes / mappings for individual terms items: defined
     * by the sourceMigration method
     */
    $this->addFieldMapping('field_medical_conditions', 1)
      ->sourceMigration('CouponConditionsMigration')
      ->arguments(array('source_type' => 'tid'));

Get it?

* Note, i am doing a 6 to 7 migration leaning on the awesome https://drupal.org/project/migrate_d2d ( not to say that Migrate ain't awesome either!)

The logic of this term mapping is correct

    $this->addFieldMapping('field_voices', 1)
         ->sourceMigration('Voices')
         ->arguments(array('source_type' => 'tid'));

But this format has been deprecated. I just tried it to solve a term matching problem I was having in a D6 to D7 migration.

You can do this in the Migrate d2d UI:

When mapping term for node in UI, map the term AND include it's source migration (important!). Next, right under the term field source destination is Option: Set to 'tid' when the value is a source ID [term_field:source_type] You should put "tid" in the Default Value column.

Here is an example.

Hi, @Pearlbear,
I need also to migrate a vocabulary with term referenced node fields to convert from a D6 to a D7 site.
Can you may be give me a plan of action how to deal with this please?
I also try this through Migrat D-D but the taxonomy fields (node/term relation) do not get migrated....
Does anyone have reusable code for this? A plain (sub)module in .zip?

Thanks a lot in advance!
Greetings, Martijn

Hi @johnvsc, and others
May be not the right issue for this, but the issue is evolving to node term references as I see.
I would very much like to migrate my referenceD terms on my nodes from D6 to D7.
With the 'standard UI' and method it seems I only get one term reference per node.
Somehow node term references from a vocabulary with multiple values enabled. Like for a Hotel; wifi, 2 beds, bath etc..only one comes true.
Does your module help with this?
Are you willing to share your whole module here?
Thanks in advance for considering this.

EDIT: It works now. I forgot to set my term_reference field to "unlimited".
Greetings, Martijn

Try and read this series of articles - https://smbjorklund.no/how-migrate-content-drupal-6-7-using-migrated2d-p... it might help.