Fast food giant McDonald's says it is "extremely disappointed" by a decision by San Francisco authorities to put the kibosh on Happy Meals and impose a ban on giving away toys with kids' meals that don't meet certain nutritional standards.

San Francisco's Board of Supervisors gave preliminary approval to the ordinance on Tuesday evening, with a vote of 8-to-3. If the law passes a second vote, the city would become the first in the U.S. to impose such a ban.

Under the ruling, scheduled to take effect in December 2011, San Francisco restaurants will be allowed to include a toy with a meal only if the food and drink in the meal contain fewer than 600 calories, less than 640 milligrams of sodium and if less than 35 per cent of the calories are derived from fat (less than 10 per cent from saturated fat), except for fat contained in nuts, seeds, eggs or low-fat cheese.

In addition, the meals must contain a half-cup or more of fruit and three-quarters of a cup or more of vegetables. A breakfast meal must contain at least a half-cup of fruit or vegetables.

Though McDonald's is not the only fast-food chain to offer toys with children's meals, the company has already come out swinging.

"We are extremely disappointed with this decision. It's not what our customers want, nor is it something they asked for," McDonald's spokeswoman Danya Proud said in a statement Wednesday.

"Public opinion continues to be overwhelmingly against this misguided legislation. Parents tell us it's their right and responsibility, not the government's, to ... to choose what's right for their children."

She added: "We are extremely proud of our Happy Meals which give our youngest guests wholesome food and toys of the highest quality. Getting a toy with a kid's meal is just one part of a fun, family experience at McDonald's."

Scott Rodrick, whose family owns half of the 20 McDonald's franchises in San Francisco, lamented after the vote that "San Francisco supervisors have taken the 'happy' out of Happy Meals."

But the man who sponsored the measure, San Francisco Supervisor Eric Mar, says the aim of the ban is to promote healthy eating habits while combating childhood obesity.

He calls the move "a challenge to the restaurant industry to think about children's health first."

"This is a tremendous victory for our children's health. Our children are sick. Rates of obesity in San Francisco are disturbingly high, especially among children of colour," said Mar.

Mar said he modelled his proposal after a similar law in Santa Clara County, Calif., adopted earlier this year. That ban applies to only a handful of restaurants in the county's unincorporated areas; San Francisco's restrictions would affect dozens of fast-food establishments.

San Francisco Mayor Gavin Newsom has promised to veto the ban. But the board is scheduled to take a final vote next week and could override that veto.