Updated 5:10pm: New Zealand Aluminium Smelters, the company behind the Tiwai Point Smelter is denying accusations of an email gag.

The E Tu union believes workers are being banned from sending emails home and sharing information with outside parties.

In a statement, Chief Executive Gretta Stephens said the company's policies haven't been altered.

She said the rights of union members to interact with their representatives are respected and honoured at all times.

She said the company recently reminded employees about appropriate use of its IT systems, in accordance with its existing policies.

Last month the company lost its appeal to the Supreme Court over a pay dispute, meaning staff will receive a share of millions of dollars worth of owed holiday payments.

Now Union E tu is accusing New Zealand Aluminium Smelters of prohibiting freedom of speech through staff emails.

It believes workers are being banned from sending emails home and sharing information with outside parties.

Organiser Trevor Hobbs thinks the company is monitoring emails, stopping staff from using it to contact the union.

He argues it's another attempt by the employer to stop the union gaining a foothold with staff, and is a breach of human rights.

SEE THE EMAIL THAT HAS CAUSED THE CONTROVERSY HERE