The apparent cost-cutting measures also apply to journeys of less than seven hours for premium economy passengers.
The reduced menu was introduced last month and came after reports the airline was going to charge for its meals.
Instead of two full meals passengers will get only one and might have to make do with snacks if they get hungrier later in the flight. The choices of alcohol and complimentary snacks will not be affected, a BA spokesman said.
Many flights from the UK to the east coast of America, including New York, take between seven and eight hours while the journey to Toronto and Montreal in Canada is around seven hours.
Spaniard Alex Cruz, 50, took over as CEO and chairman of BA in April, having started his career with American Airlines in 1995.
British Airways reported total profits after tax of STG2.5 billion ($A4.22 billion) for the year ending December 2015.
A BA spokesman said: "We offer customers on all of our transatlantic flights a three course meal, bar service and snacks and on our longer transatlantic flights, including to the west coast, customers are offered an extra meal during the flight.
"We regularly review our catering to ensure we are investing where it matters most to our customers."
