DETROIT — Ford Motor said on Tuesday that it would build a new assembly plant for small cars in Mexico, continuing a trend of automakers increasing production there because of lower wages and favorable trade laws.

Ford, the nation’s second-largest auto manufacturer, said it would invest $1.6 billion to construct a plant that will employ 2,800 workers and begin making vehicles by 2018.

Several auto companies are expanding operations in Mexico, which has become a major auto manufacturing center. Last year Mexico produced 3.4 million vehicles, of which about 80 percent were exported to the United States and elsewhere.

But Ford alone has been singled out for criticism by the Republican presidential candidate Donald J. Trump for its aggressive expansion in Mexico, which also includes new investments in factories that make engines and transmissions.