In the seven years that he has been France’s president, Emmanuel Macron has bet on tax cuts for the wealthy and for corporations as a recipe for stimulating the economy. His new government is about to tear up that playbook.

Faced with a rapid deterioration in the nation’s finances, Mr. Macron’s recently appointed prime minister, Michel Barnier, is opening the door to higher taxes on businesses and the rich, in a last-ditch bid to plug France’s widening budget deficit and reassure worried international investors about the government’s ability to tackle the problem.

Mr. Macron is under pressure to act quickly. Borrowing costs for France, which has Europe’s second-largest economy after Germany’s, soared Tuesday to their highest level since the 2008 financial crisis, as investors increased the premium they demand to hold French debt. The government is facing an uphill battle to control a ballooning debt and deficit that have become among the highest in Europe.

Warning that France’s financial situation had worsened rapidly, Mr. Barnier said on Sunday that he would open the long-taboo subject of reversing several of Mr. Macron’s signature tax cuts, despite pledges from the president just a few weeks ago not to lift taxes.

“I’m not going to raise taxes on all French people,” Mr. Barnier said in an interview on French television. “But I cannot exclude the wealthiest and corporations from the national effort to rectify the situation.”

How did France reach this critical point?