Plymouth-based Travel Leaders Group is gaining more than $850 million in annual sales volume with the merger of its largest New York-based agency with another New York agency. Travel Leaders' wholly owned Tzell Travel Group and Protravel International Inc. have agreed to merge, the Minnesota firm announced this week.

Combined, the two agencies will provide $2.35 billion in annual sales to Travel Leaders' nearly $17 billion in sales volume. The merger is pending government antitrust approval and is expected to close in November. The two privately held companies did not disclose the full terms of the transaction.