The Association of Canadian Travel Agents (ACTA) is calling for an investigation into an on-line seat sale by Air Canada.

The carrier is offering purchasers on-line-only deals of up to 50 per cent off regular prices.

ACTA says the sale has travel agents across the country upset.

The on-line seat sale began on August 2 and ends August 14.

It's the first time Air Canada has offered a seat sale that is exclusively on-line.

This means that people booking flights through travel agents can't take advantage of the sale.

The Association of Canadian Travel Agents has written to both the Minister of Transport and the federal Competition Commissioner, asking for an investigation.

ACTA president Randy Williams says the on-line-only seat sale is possible because Air Canada has no real competition.

"We don't believe that Air Canada would have attempted this if there were competitors," Williams says, "because they certainly would know that agency response would be to refer customers to alternative carriers."

He says Air Canada risks damaging its relationship with travel agents.

Air Canada says it values that relationship, but that it has to find more cost effective ways of selling its tickets.

Airline spokesperson Renee Smith-Valade says the on-line sale is what customers have been asking for.

"Customers are telling us that they expect that Air Canada will be current and use current practices and offer this type of an initiative," she says.

"And so we have chosen to do so while still being very careful to maintain our very positive working relationship with the travel agency community."

Smith-Valade says Air Canada will continue to offer sales through travel agents as well as on-line.