Vietnamese trade union official Wang Yi said the party’s decision to expel the trade union leader, Le Quang Binh, is “not a good beginning”.
He said Mr Binh had not shown his party’s loyalty to the trade unions.
“We are concerned about the party and its leadership,” Mr Wang told the BBC.
Mr Binh’s removal was announced on Wednesday night, after he refused to apologise for the attack on a Vietnamese worker.
Vietnam’s government has faced criticism for its handling of the attack, with the UN and human rights groups accusing the government of ignoring warnings and allowing the attack to continue.
A UN panel last week said the attack was “inhumane and in breach of international humanitarian law”.
VnExpress has contacted the National People’s Congress (NPC) for comment.