Morgan Stanley has imposed financial penalties on employees who used messaging platforms such as WhatsApp for company business, according to two sources familiar with the situation.

The penalties ranged from several thousand dollars for some staff to more than $1 million for others. The amounts were determined by factors such as the number of messages sent, seniority and whether the employees had already received warnings, according to one source familiar with the matter.

The Financial Times reported on the penalties earlier Thursday.

The move comes after the lender had agreed to pay $200 million to the U.S. Securities and Exchange Commission in 2021 to resolve probes into employee communications on messaging platforms that had not been approved by the company.

Wall Street's self-regulatory body — the Financial Industry Regulatory Authority — requires broker-dealers to keep records of all business-related communications. The SEC has been looking into whether lenders have been keeping a track of employees' digital communications.

In September, the SEC fined 16 financial firms, including major global banks, a combined $1.8 billion after staff discussed deals and trades on their personal devices and apps. The probe has since expanded beyond broker-dealers to investment funds and advisers, according to four people familiar with the inquiry, Reuters reported in October.

Some banks that were fined have told employees that future pay and bonuses will be docked for those who are found to have used unauthorized communication channels, said a source familiar with the situation.

Financial firms are also scouring employees' phones and personal computers in a widespread effort to demonstrate to regulators that they are punishing breaches of communications policies, the source said.

In 2020, two senior Morgan Stanley executives left the bank after unauthorized use of WhatsApp to discuss work matters.