Citadel is preparing to take a much harder line over the SEC's widening Wall Street WhatsApp probe than the almost two dozen banks that have already agreed to hefty settlements during the past two years over staff use of the messaging app, according to a report by Bloomberg.

The report cites unnamed sources familiar with the matter as revealing that Ken Griffin’s hedge fund firm has told industry peers that it plans to challenge the SEC if the regulator moves against it, and will resort to taking the commission to court.

The Miami-based firm would likely argue that as a hedge fund it isn't subject to the same rules as Wall Street banks including JPMorgan Chase & Co and Bank of America Corp, which have agreed to pay more than $2.5bn in settlements over employees' use of unofficial messaging platforms for business.

Bloomberg reported in February the hedge fund was under SEC investigation for alleged unmonitored communications, though the agency has yet to formally bring an action against Citadel, and could yet decide not to act, according to a Bloomberg source.