A car industry union has called on the federal government to investigate the treatment of workers on 457 visas at an Adelaide workplace, alleging one was sacked after joining the union.

The Australian Manufacturing Workers' Union (AMWU) has also called on the government to waive the 28-day deportation rule while Fijian Mohammed Khan fights his sacking in the Federal Court.

Union members and officials rallied outside Mr Khan's former workplace, Adelaide Isuzu, on Thursday in support of their colleague, who they said had been denied his basic human rights.

AMWU national president Paul Bastian said under the 457 visa system workers were bonded to employers and if they left or were sacked they only had 28 days to find new work before facing deportation.

"So that's the sort of control and economic power bosses wield under this system," he said.