TORONTO (CP) -- Air Canada is warning that a group of disgruntled pilots has threatened to delay flights as part of an escalating protest over seniority rankings, the Globe and Mail reported Monday.

Air Canada chief operating officer Rob Reid said in an internal letter to the company's 3,000 unionized pilots that he's concerned about job action by those belonging to the so-called Original Air Canada group.

The pilots were hired by Air Canada before its merger with Canadian Airlines International Ltd. in 2000.

''Several of our pilots have communicated to their co-workers and called for action to slow down the company's operations,'' Reid wrote. ''We are all professionals and I know that the vast majority of you do not condone or support this activity. Whenever such activity happens by a few, we all suffer the consequences _ company, pilots and fellow employees alike.''

The airline told the Canadian Industrial Relations Board late Friday that OAC e-mails encourage pilots to engage in a number of work-to-rule tactics, including ignoring the phone when on call, temporarily resigning supervisory duties, showing ''renewed vigilance'' in following ''professional standards of conduct'' and re-examining their health to see whether they're ''fit to fly'' or are suffering from ''fatigue.''

Such tactics constitute an ''illegal strike, with sick-ins and refusal of flights,'' according to Air Canada, which emphasized that for now, operations have not been disrupted.

Members of the Air Canada Pilots Association recently rejected a proposed labour contract because they wanted to call attention to their anger over many former Canadian Airlines pilots moving ahead of them in seniority rankings in 2003.