An Australia Post spokeswoman said Oliveira was terminated from his A$70,000 ($74,827)-a-year role for "breaches of his contract relating to safety".
"Oliveira has been dismissed for repeatedly failing to meet his obligations as an Australia Post employee with multiple breaches of his contract of employment over a period of time," she said.
"These include serious safety breaches involving a forklift. The safety breaches included an incident of causing damage to a truck and then using the forklift to attempt to fix the damage, and a second incident where a forklift was driven into rubbish bins."
Documents provided to news.com.au show Oliveira was subject to an earlier disciplinary decision over a safety incident, but the outcome was he was transferred to a different role and ordered to undergo medical checks.
His April 10 termination letter makes no mention of safety breaches.
It instead says he breached Australia Post's "Our Ethics" guidelines when he "provided video footage" and "false information" to news.com.au.
"Your unacceptable behaviour includes but is not limited to … intentionally or recklessly engaging in conduct that damages our interests, employee relations or public reputation," the letter said.
His unacceptable behaviour also included "intimidating, offending or misleading customers, colleagues, suppliers or the public" and "starting or spreading rumours that may damage another person's reputation, including when using social media".
"My decision is that your conduct in relation to the matters identified above constitutes serious and wilful misconduct and that you be dismissed from Australia Post," the letter said.
Oliveira, who worked at Australia Post for nearly eight years, says he's "not feeling the best, to be honest" and needs to find another job soon to pay his bills.
In the meantime, he will take his case to the Fair Work Commission. "These guys are bastards," he said. "You obey the law by reporting a crime and they punish you."