Fast-food workers from three dozen U.S. cities on Wednesday will protest at the headquarters of McDonald's Corp (MCD.N), calling for a significant wage hike, as company shareholders also prepare to weigh in on the pay of the fast-food giant's top executives.

The latest, and possibly largest, protest against the global chain comes a day ahead of a shareholders vote on executive pay at McDonald's, where Chief Executive Don Thompson took home total compensation of $9.5 million in 2013.

Low-wage U.S. restaurant and retail workers are calling for a rough doubling of pay to $15 per hour and the right to unionize. Their frequent protests have helped fuel a national debate on income inequality at a time when many middle- to low-income Americans are struggling to make ends meet.

Jessica Davis, a 25-year-old McDonald's crew trainer with two children, said CEO Thompson is earning his millions on the backs of working mothers and fathers.

Davis, who works at a company-owned McDonald's in Chicago, says she earns $8.98 per hour and works part-time despite requests for more hours.

"We need to show McDonald's that we're serious and that we're not backing down," said Davis, who plans to join Wednesday's protest.

McDonald's, which is grappling with sagging U.S. sales and profit-crimping beef price spikes, does not disclose average pay for restaurant workers, most of whom work for McDonald's franchisees.

According to the Bureau of Labor Statistics, the 3.5 million fast-food and counter workers in the United States earn a median hourly wage of $8.83, or almost $18,400 per year based on a 40-hour work week without vacation.

Demos, a public policy think tank in New York, said fast-food workers are the U.S. workforce's lowest paid occupation. A Demos report found that the CEO-to-worker compensation ratio for the fast food industry was more than 1,000-to-1 in 2013.

Chipotle Mexican Grill (CMG.N) shareholders, in a non-binding vote, on May 15 came down more than 3-to-1 against the advisory pay proposal from the popular burrito seller, where co-CEOs Steve Ells and Monty Moran received total 2013 compensation of $25.1 million and $24.4 million, respectively.

U.S. President Barack Obama has pushed Congress to raise the federal minimum wage to $10.10 per hour from the current $7.25, a move fought by Republicans in Congress.

Twenty-one states and Washington, D.C. have minimum wages higher than the federal minimum wage, and 38 states have considered minimum wage bills during the 2014 session, according to the National Conference of State Legislatures.