Canada's transport regulator has asked Air India to investigate an incident of a pilot who was removed from a plane before it was due to take off and found to be under the influence of alcohol, a person familiar with the matter said.

Two breathalyser tests conducted by Canadian police at Vancouver International Airport showed the pilot was unfit for duty, the person said on Friday. The incident was labelled as a "serious matter" by Transport Canada in a letter to Air India and authorities are likely to pursue enforcement action, the person added.

The person requested anonymity as they were not authorised to speak to the media. Transport Canada did not respond to an emailed request for comment outside regular working hours.

In a statement, Air India said the flight from Vancouver to Delhi on December 23 experienced a last-minute delay due to the incident, adding that an alternate pilot was brought in to operate the flight. The airline said Canadian authorities raised concerns about the pilot's fitness for duty but did not provide details.

"The pilot has been taken off flying duties during the process of enquiry. Air India maintains a zero-tolerance policy towards any violation of applicable rules and regulations," Air India said.

"Pending the outcome of the investigation, any confirmed violation will attract strict disciplinary action in line with company policy."

The aircraft was a Boeing 777, a model that can seat up to 344 passengers, according to the websites of Flightradar24 and Air India.

The letter from Transport Canada official Ajit Oommen has asked Air India to provide its findings and details of steps taken to prevent future occurrences by January 26, the person familiar with the matter said.

Air India has been under intense scrutiny since the June 12 crash of a Boeing Dreamliner killed 260 people. India's aviation regulator has flagged multiple safety lapses at the airline, which was previously owned by the government until 2022.

Pilots at Air India, owned by Tata Group and Singapore Airlines have also come under scrutiny. This week, India's Directorate General of Civil Aviation (DGCA) sent warning notices to four Air India pilots, flagging "serious safety concerns" related to regulatory compliance and flight crew decision-making.

The DGCA said the pilots accepted an aircraft for operation last year despite prior knowledge of "repeated snags" and "existing systems degradations," according to warning notices dated December 29 seen by Reuters. The aircraft is a Boeing 787 used for long-haul flights, according to Flightradar24.

Earlier this year, the DGCA proposed tightened rules on alcohol testing for crew members, including one that would have a pilot lose their license permanently after three positive tests. Current rules require post-flight breath-analyzer examinations for each trip to be carried out at the first port of landing in India.

Canadian rules state that a pilot cannot operate an aircraft within 12 hours of consuming an alcoholic beverage.