A Perth panel beater has been fined more than $40,000 for sacking a long-term worker diagnosed with cancer.

The Federal Court had heard the long-term employee told his boss at AJR Nominees, Pasquale Minniti, that he had cancer in 2010.

Mr Minniti later accused the employee of making up his illness, and in 2011 he fired the employee.

The Federal Court found he pressured his worker to resign in a "concerted campaign" over six weeks to prevent him from taking sick leave.

Justice Gilmore found that the employee was sacked when he was vulnerable, suffering financially and at a time when he was confronting a serious medical condition.

Meanwhile, the Fair Work Ombudsman has found that the employee was not paid out sick leave, wages in lieu or annual leave entitlements valued at around $16,000.