Austal USA broke U.S. labor laws by firing 10 workers and threatening plant closure, job loss and stricter discipline in its anti-union drive five years ago, the National Labor Relations Board has ruled.

The board affirmed an earlier ruling by a judge that also ordered a new union vote at Austal’s shipyard in Mobile, Ala. The NLRB said the Australian firm behaved in an objectionable manner by placing security guards at the gate of the plant on the morning of the failed 2002 vote.