LONDON (Reuters) - Commodities trading company Trafigura has extended the notice period for traders leaving the firm to a minimum of six months or up to one year, three sources with knowledge of the matter said, after recent employee departures.

It is not known exactly when changes were made to extend the notice period, but the sources said they apply to new and existing employees and depend on seniority levels.

A longer notice period could discourage traders from applying to work at Trafigura, one of the sources said.

Trafigura declined to comment.

Energy traders including Mercuria, Gunvor and Vitol are returning to trading in metals after an absence of many years, looking to diversify from oil and cash in on a bonanza they expect to be created by demand for clean energy transition and wider use of artificial intelligence.

They have made hefty profits from fossil fuels such as oil and gas, prices of which rocketed in the aftermath of Russia's invasion of Ukraine in February 2022.

Leaving Trafigura and joining Mercuria in recent months are Mehdi Wetterwald in Geneva, Michaela Dempsey in the United States and Leonard D'Offay in Dubai, according to their LinkedIn profiles. 

They are joining ex-Trafigura trader Kostas Bintas at Mercuria.

Wetterwald, Dempsey and D'Offay did not immediately respond to requests for comment on LinkedIn.

Mercuria declined to comment.

Trafigura in June sent a letter to current and former employees proposing share clawbacks for breaches of confidentiality and its code of conduct.

Clawbacks are typically used by financial firms which require money already paid out to employees to be returned in the event of misconduct or poor performance.