British Airways is among the airlines cancelling US flights due to 5G safety concerns.
The action is in response to fears that the activation of the C-band strand of the mobile phone service near US airports on Wednesday could disrupt planes' navigation systems.
Boeing 777s are thought to be particularly at risk of being affected.
The introduction of the technology has been halted in some parts of the US, but is going ahead elsewhere. Britain's Civil Aviation Authority (CAA) said it has "issued safety advice" to airlines.
British Airways cancelled a handful of flights from Heathrow to Boston, Chicago, Los Angeles, New York, and San Francisco on Wednesday.
The airline said in a statement: "Safety is always our priority. We are monitoring the situation in the US closely and will continue to review our schedule in the next few hours."
"We're disappointed that some of our customers are facing potential disruption and will update them as soon as possible on any changes to their travel plans."
The carrier said some flights due to be operated by Boeing 777s are using different, larger aircraft such as the Airbus A380 to ensure people can still fly on the same day they booked.
Other airlines have made many more cancellations.
Emirates suspended all its flights to nine US airports on Wednesday "until further notice."
The Dubai-based carrier told customers the measure was "due to operational concerns associated with the planned deployment of 5G mobile network services in the US at certain airports."
It added: "Emirates regrets any inconvenience caused. We are working closely with aircraft manufacturers and the relevant authorities to alleviate operational concerns, and we hope to resume our US services as soon as possible."
Other airlines to cancel flights include Air India, Japan-based ANA, Japan Airlines, and Korean Air.
Virgin Atlantic, which does not operate Boeing 777s, said it has not made any cancellations or aircraft type changes.
The concern about 5G in the US relates to its potential effect on aircraft altimeters, which measure altitude. This does not have an impact on British airports because the US uses a different frequency for 5G.
A CAA spokesperson said: "There have been no reported incidents of aircraft systems being affected by 5G transmissions in UK airspace.
"We are working with Ofcom and the Ministry of Defence to make sure that the deployment of 5G in the UK does not cause any technical problems for aircraft and are keeping our position under constant review.< ``
"Also, as UK aircraft fly throughout the world we have issued safety advice to airlines on the 5G status in other countries, including the USA."
