Mayor Eric Garcetti signed into law on Saturday an ordinance that makes Los Angeles the biggest city in the nation to gradually raise the minimum wage to $15 an hour.

He called the law "a major victory for our city" at a signing ceremony in south Los Angeles, and said the wage increases will enable working families to lift themselves out of poverty.

"LA as a whole will benefit from this boost: We have always prospered the most when everyone is able to spend money into our economy," Garcetti said.

The law will boost the minimum wage to $10.50 in July 2016, followed by annual increases to $12, $13.25, $14.25 and $15. Small businesses and certain nonprofits get an extra year to phase in the increases.

Calls for raising the minimum wage have grown as the nation struggles with fallout from the recession, worsening income inequality, persistent poverty and the challenges of immigration and the global economy.

Seattle and San Francisco also have phased-in minimum wage laws that eventually require hourly pay of $15 an hour, or annual pay of about $31,200 for a full-time job. Last year, Chicago passed a phased-in minimum wage increase to $13 an hour.

Last week, the California Senate approved a plan to raise the statewide minimum wage again, lifting it to $13 an hour in 2017 and tying it to the rate of inflation after that.