Prince Harry and Meghan have previously spoken a lot about climate change and the need to protect the environment.
In June, they posted on their Instagram page: "With nearly 7.7 billion people inhabiting this Earth, every choice, every footprint, every action makes a difference."
But, now it's been reported that the royal couple recently used a private jet to go on holiday to Nice in the South of France.
Some people don't think they should have travelled this way because of the damage flying can do to the planet.
Private jets usually carry fewer passengers than commercial planes, meaning they burn much more fuel per person per hour.
Planes contribute to climate change because they give off a range of greenhouse gases and the main one is carbon dioxide. People have said Prince Harry and Meghan should be setting a better example by choosing other ways to travel.
The Duke and Duchess of Sussex stayed at Elton John's house in France - he's a famous singer and wrote the music for The Lion King.
He's defended their use of his jet and said he paid for it to give them some privacy.
The singer also said he paid money to compensate for any carbon emissions produced from their flight.
Buckingham Palace have declined to comment.