"I openly call for taxing polluting activities to invest in the ecological transition," said Beaune, adding that the government plans to increase the tax on flights departing France to fund rail investments.

I don't think it's entirely clear what he wants the EU to do, but it really seems like making other forms of transport cheaper is part the goal here.

Hence I think it's likely going to be a reasonable proposal. Making flights more expensive to pay for cheaper trains is a good way to go about it. The money for the trains to come from somewhere and flights are something people can live without.