PARIS — French political parties of the far right and the far left are making election promises that are appealing — and expensive. And they’re rattling the rest of the European Union and global markets.

Vying to oust the centrist government of President Emmanuel Macron in an upcoming two-round parliamentary election June 30 and July 7, French political parties are vowing to cut gasoline taxes, let workers retire earlier and raise wages.

Their campaign pledges threaten to bust an already-swollen government budget, push up French interest rates and strain France’s relations with the…