The T. Rowe Price Group banned around 1,300 employees of American Airlines from trading the funds in their 401k plans. Sources from the airline company and retirement plan administrator JPMorgan Chase & Co told Reuters that 800 more employees had also been warned by the investment firm about their trading patterns.

T. Rowe Price said the subscribers were engaged in collective trading. Bill Benitende, spokesman for T. Rowe Price, confirmed the ban. He also told Reuters through an emailed statement that collective trading can increase the costs for long-term investors. He said that that it could also upset the strategies of investment managers. Collective trading by a group could compel managers to make untimely buying and selling decision.

Subscribers of an investment newsletter sent to American Airline employees were the subject of the ban. T. Rowe Price had earlier imposed temporary restrictions on the trading of some AA employees who subscribed to the EZTracker newsletter. Now, the ban issued by T. Rowe Price was permanent.