* Gupta brothers are friends of ousted president Zuma
* Under investigation over alleged corrupt links to Zuma
* Workers at their coal mines worried over salaries (Recasts with Gupta companies filing for creditor protection)
JOHANNESBURG, Feb 23 (Reuters) - At least eight companies owned by the wealthy Gupta family accused of corrupt ties to former president Jacob Zuma, have filed for protection from creditors, documents showed on Friday.
The Indian-born billionaire business associates of Zuma, were accused of using their political connections to win state contracts and influence cabinet appointments, in a report by an anti-graft watchdog in 2016. Zuma and the Gupta brothers deny any wrongdoing.
The Companies and Intellectual Property Commission (CIPC), South Africas companies registry office, shows on its website that eight firms owned by the Gupta's sought protection from creditors on Feb. 20, including Optimum Coal mine, which has faced a strike by its workers this week over unpaid salaries.
Another mining operation, Koornfontein Mine, is also listed, along with Optimum Coal Terminal and Tegeta Exploration and Resources in the coal sector.
"It was inevitable that the empire would implode," Ben Theron, chief operating officer of the Organisation Undoing Tax Abuse whistleblower group said in a statement.
The other firms are Shiva Uranium, VR Laser, Islandsite Investments One Hundred and Eighty, Confident Cocepts.
Last week, South Africa's elite police unit, the Hawks, raided Gupta properties as part of investigations into their alleged corrupt dealings. Ajay Gupta was declared "a fugitive from justice" by South Africas chief prosecutor last week after he failed to report to police investigating corruption allegations.
South Africa's National Union of Mineworkers (NUM) said its members had not been paid on time at the Gupta's Optimum coal mine and would not return to work. It also said more than 500 workers will strike on Monday at Koornfontein Mine over pay.
NUM spokesman Livhuwani Mammburu said the union's members were concerned the non-payment of salaries was linked to India's Bank of Baroda cutting ties with the Gupta family's operations.
Baroda was the last bank to service Gupta companies. South Africa's main commercial banks have all cut ties with the Guptas, citing reputational risk.
"The guys were not paid and they want a meeting with the CEO because they are concerned about the business rescue proceedings which they were not informed about," Mammburu said, referring to workers at Optimum Coal.
The Optimum Coal mine supplies the fossil fuel to the Hendrina power station, while Koornfontein feeds coal to Eskom's Komati power station. Both are part of the network of state-run utility Eskom which provides virtually all of the electricity for Africa's most industrialised economy. (Additional reporting by Ed Stoddard and Tanisha Heiberg; Writing by James Macharia; Editing by Elaine Hardcastle)