Democratic White House hopefuls are increasingly showing up at protests by McDonald's workers demanding higher wages and the right to unionize.

As the country's second-biggest employer, the fast-food chain is a frequent target of labor activists and Democrats seeking office.

The Fight for $15 movement began in 2012, and the Democratic Party's official platform now includes a commitment to a $15 federal minimum wage.

While President Donald Trump is known for touting his fondness for fast food, his would-be Democratic replacements are increasingly highlighting the poor pay and working conditions of the industry's workforce. And that's making McDonald's a favored target.

Senators Kamala Harris and Cory Booker, Mayor Pete Buttigieg and former Representative Beto O'Rourke last week joined demonstrating McDonald's workers in Las Vegas. And Harris, along with Senators Elizabeth Warren, Amy Klobuchar and Bernie Sanders, as well as former Housing and Urban Development Secretary Julián Castro were among those recently calling on McDonald's to require its franchisees do more to protect workers from harassment.

McDonald's workers were front and center in the Fight for $15 movement that erupted in 2012. Now, the notion of a $15 minimum wage is a popular one not only for progressive activists but for Democrats holding or seeking office. The alliance is a logical one. Fight for $15 activists were knocking on doors in 11 states in an effort to elect candidates last November who would support workers' rights, and the Democratic Party's official platform now includes a commitment to a $15 an hour minimum wage.

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"There is a renewed Interest among Democratic candidates in labor, which is not unusual on the eve of a presidential election," Harley Shaiken, a labor relations professor at the University of California at Berkeley, told CBS MoneyWatch. "Labor is a powerful force in any election, and this election in particular." Shaiken cited "out-of-control inequality, issues related to trade and the well-being of working families as very central."

"Something else is often ignored: renewing the right of workers to organize, which is still on the books, but largely erased in practice," Shaiken said. "The safeguards for organizing have been really stretched, said Liesl Orenic, a labor historian at Dominican University in Illinois.

In response, McDonald's said the burger chain does not control the wages its franchisees pay. "The average starting wage at corporate-owned restaurants exceeds $10 per hour, and we believe the average starting wage offered by those independent business owners is likely similar," a spokesperson emailed.

"McDonald's recognizes the rights under the law of individual employees to choose to join -- or choose not to join -- labor organizations," the company spokesperson said.

Critics heard

McDonald's, the nation's second-biggest private employer, routinely draws negative attention from labor groups and pro-labor politicians, as do other corporations, including Walmart and Amazon. Senator Sanders showed up at Walmart's annual shareholders meeting earlier this month in Arkansas to call on the nation's biggest employer to raise wages for its 1.5 million U.S. workers.

Sanders is a frequent critic of retailers and fast-food companies, saying they don't pay employees enough to live on. He has regularly called out large companies for reaping profits while paying wages that leave many workers dependent on taxpayer-funded public assistance programs.

Walmart hiked its starting pay to $11 at the beginning of the year, and CEO Doug McMillon called for an increase in the federal minimum wage, labeling $7.25, unchanged since 2009, as "too low." Amazon in October 2018 hiked its minimum hourly pay to $15, with CEO Jeff Bezos declaring "we listened to our critics."