Rogers Sportsnet in Toronto reported Saturday (http://bit.ly/1Ka47Aw ) that online flight records showed the Flyers took a flight from Philadelphia to Nashville the night of Dec. 26.
Players are barred from travelling or practicing from Dec. 24-26 under the collective bargaining agreement.
The person who confirmed the union investigation spoke on the condition of anonymity because the NHLPA has not publicly commented on the report.
Bill Daly, the NHL's deputy commissioner, declined comment.
Flyers spokesman Zack Hill said the team had no comment.