The 26-year-old man, Marcin Wilk, claims that Polish and Bulgarian employees at the zoo in eastern Sweden were treated badly while he worked there in 2011.
The foreign workers had lower wages and worse work conditions than their Swedish colleagues, according to Wilk.
In December 2012, the Kalmar District Court heard tape recordings of zoo managers shouting abuse at Wilk.
"You think you're better than others. Take your things and go to hell. You're behaving like a damn monkey," they said when firing Wilk.
"Poles only have the rights granted to them by Barbro Hägg," Wilk told the Barometern newspaper, referring to the zoo's CEO.
"It's like an old-fashioned feudal system."
Wilk, who has represented himself in the legal proceedings, claimed that he and other Poles worked 10-hour days seven days a week while Swedish employees had a regular 40-hour work week.
While Swedes were paid 14,000 kronor ($2,160) per month, the Polish workers got 6,800 kronor plus room and board.
"I was discriminated against on the basis of my nationality. But everyone who works with discrimination issues knows that it is hard to prove. Discrimination is hidden," said Wilk.
At the time of his dismissal, Wilk had failed to show up to a meeting about security at the zoo, but claimed he had not been told about the meeting.
He secretly recorded a shouting match in which a man yelled at him, accused him of having a superior attitude and called him a "monkey".
Wilk was asked several times to take his belongings and leave. He was also warned that he would not receive his last wages if he refused to sign his termination notice.
Swear words and condescending language could be heard in the taped conversation, according to the paper.
Wilk is asking for 1 million kronor in damages.
The zoo has denied the allegations but the LO union confederation said it is not unusual for foreigners to have worse work conditions than Swedish citizens.
The Kalmar District Court is expected to issue a verdict on Monday.
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