MONTREAL -- Customer service representatives at Air Canada were inadequately trained on a new digital booking system, and their lack of training has contributed to a backlog in customer service calls, sources inside Air Canada told CTV News.

The sources, who have direct knowledge of the system and work with employees who use it daily, said that customer service representatives received only one week of training to use the new system, and that training was not specific enough to use the system effectively.

The new booking system is more modern than the previous system, which was 25 years old, Air Canada says.

But a source said it is distinctly different from what was used before and is more time-consuming, leading to delays in customer dealings.

In the days following its implementation, customer service representatives were stressed and anxious coming to work, one source said.

Frustrated passengers were often on hold for hours before reaching a customer service representative, and booking problems have been more challenging and have taken longer to resolve, the source added.

Fewer calls from passengers are processed every hour, another source said.

Angry passengers have taken to social media in droves to complain of their inability to reach Air Canada to discuss their bookings.

As the holiday season - one of the busiest times of the year for air travel - approaches, the sources fear the problems will get worse.

CTV News is not revealing the identities of the sources because they were not authorized to speak to the press; they also feared repercussions from the company.

Recently, Air Canada’s customer service line stopped putting callers on hold. Instead, an automated message greets callers. CTV News recently called and could not get through to a representative.

“Air Canada has recently introduced a new reservation system, and call volumes are significantly higher than normal. Due to current volumes, I apologize that we are unable to place you on hold at this time,” the message said. “… I sincerely apologize for the delay in reaching us today, and I thank you for your understanding.”

The message was repeated in French and looped.

In a statement sent to CTV News, Air Canada admitted that customers were encountering technical difficulties as a result of the new system.

“This has been a massive, two-year project involving 700,000 hours of development time. Since the beginning, we have had a considerable team of in-house IT experts and international reservation system professionals dedicated to this project, and they remain engaged. As with any IT project of this magnitude and complexity, some temporary issues are inevitable,” the statement reads.

The airline transitioned to the new IT system on Nov. 18. “It will bring many advantages for customers' travel agents and our employees once fully in place,” the airline told CTV News this week. “For example, we will be able to better help customers during storm disruptions and work much more easily with our main airline partners around the world, creating a better travel experience.”

The company said it had hired staff in an attempt to reduce passenger call backlogs, but they added that the number of customers affected is relatively small.

“The new system is functioning largely as expected,” they wrote.

But some passengers have said the migration to the new system has made it more difficult to use and even changed their reservation information.

When questioned about the difficulties faced by their customer service representatives, the company added: “We thank our employees for their dedication and professionalism in serving our customers.”