Retailers feature plus-size models. "Fat influencers" have seen success on social media. Doctor groups have framed obesity as a disease that goes beyond willpower.

But public attitudes about weight have become more negative, even though thin people make up the minority of the population, according to a recent study from Harvard University. People who are overweight or obese not only have emotional and physical difficulties after being bullied about their weight, but also suffer financial penalties. Research from the Rudd Center for Food Policy and Obesity at the University of Connecticut found heavier workers earn less than thinner employees, are less likely to get promoted, and are viewed as lacking discipline.

"Weight bias happens at virtually every state of the employment cycle, from being hired to getting fired," said Rebecca Puhl, deputy director for the Rudd Center.

Michigan is the lone state with a law prohibiting discrimination on the basis of weight, and lawmakers in Massachusetts are seeking to follow along. A handful of cities, including San Francisco and Washington, D.C., also have such laws.

Despite the dearth of rules, the issue of weight discrimination in the workplace is gaining some attention from high-profile court cases. This summer, the Washington state Supreme Court ruled it was illegal under state law to refuse to hire someone just because of obesity, saying that employers were violating laws that prohibit discriminating against someone with a physical impairment. Over the years, waitresses and cheerleaders have sued against workplace rules on appearance.

In some jobs, such as for the military or in fire departments, workers must meet certain fitness requirements. In general, however, lawyers advise workplaces to avoid discussing weight unless they can show how it directly relates to workplace safety and an individual's ability to do a job.

That can make weight bias cases harder to prove, and when discrimination does happen, plaintiffs face limited legal recourse. The Equal Employment Opportunity Commission, the federal agency that investigates allegations of workplace discrimination, addresses bias tied to race, color, gender, age, religion, national origin, and disability. While weight isn't on that list, sometimes people file weight-related complaints by alleging gender or disability discrimination.

For example, in 2017, bus driver Mark Richardson accused the Chicago Transit Authority of firing him because he was obese and sued under the Americans with Disabilities Act. Richardson had been 594 pounds, and his employer determined his weight prevented him from safely driving a bus. The court ultimately decided that obesity itself didn't qualify as a disability unless caused by an underlying physiological disorder.

In other cases, complaints tied to weight are filed under gender discrimination because women tend to be targets of weight bias more than men. That's partially why many workplaces tend to be more indirect about weight requirements.

"In my experience, it’s not often a written policy, because those ideas about what size a person can be opens up employers to gender-based discrimination," said Ted Kyle, who is on the board of directors for the Obesity Action Coalition. "But it can often be fairly explicit in terms of people being told that their appearance is holding them back in terms of progressing their career."

Sarah Bramblette knows what it's like to get that kind of feedback. Several years ago, when she was working at a medical billing office and was 200 pounds overweight, her supervisor told her in a performance review that she was working above expectations but that she should have a more professional appearance.

Bramblette has medical conditions that cause tissue and fluid to accumulate in her arms and legs, making it painful to wear certain types of clothing. Still, she dressed up even more for work but was passed up for a promotion. After that, she took the advice she had received about her appearance as a veiled reference to her weight.

Puhl from the Rudd Center thinks adding weight as a protected class would help to prevent discrimination and allow for workplaces to warn workers not to harass each other over weight.

"Adding weight legitimizes this as a form of discrimination, otherwise it makes it seem as though it's OK to tolerate," Puhl said.

Surveys published in the Journal of Obesity show nearly 80% of the public agrees. But under U.S. labor "at-will employment" laws, workers can be fired at any time and for any reason. Workers in unions are more protected, as are people who fall under protected classes, but some are more cautious about calls to expand the protections further.

"There is no question that, in our society, people are often judged unfairly on account of their weight or their looks, and I have a great deal of empathy for people who have been treated unfairly on that basis," said Jennifer Braceras, director of the Center for Law and Liberty at the Independent Women's Forum. "But I would caution lawmakers to think long and hard before creating yet another protected class."

She added: "Historically, American anti-discrimination law has been used to prohibit and punish discrimination on the basis of immutable characteristics. It was never intended to eliminate at-will employment."