DETROIT — When union contracts were finally ratified at Ford Motor and General Motors last week, a new era began in the American auto industry.

The deals, which culminated labor talks among the nation’s three big automakers, were the most generous for workers in more than a decade and represented a striking shift from years of cuts and stagnant wages.

“The feeling among workers was that if you’re not going to get the money now when we are near the top of the market, you’re not going to ever get it,” said Kristin Dziczek, a labor analyst at the Center for Automotive Research in Ann Arbor, Mich.

But for automakers, the pay raises will add to the pressure to maintain profits and could spur a shift of less-profitable car production to Mexico from the United States.