Sen. Bernie Sanders on Wednesday said he stands in "solidarity" with the Uber and Lyft drivers going on strike.

Drivers across the country are striking over work conditions and pay rates.

"Uber and Lyft drivers are struggling as they work for billion-dollar companies," Sanders said in a tweet. "These drivers are not 'independent contractors'—they are employees who deserve rights and benefits. I stand in solidarity with them as they strike today for a dignified life."

Sanders has routinely criticized big companies like Amazon, Walmart, and Disney over their treatment of workers — particularly when it comes to pay. He's pushing for a $15 federal minimum wage.

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Sen. Bernie Sanders of Vermont expressed support for Uber and Lyft drivers going on strike on Wednesday over work conditions and pay rates.

"Uber and Lyft drivers are struggling as they work for billion-dollar companies," the presidential hopeful said in a tweet on Wednesday. "These drivers are not 'independent contractors'—they are employees who deserve rights and benefits. I stand in solidarity with them as they strike today for a dignified life."

Wednesday's comment is in line with Sanders' routine criticism of mega-companies like Amazon, Walmart, and Disney over their treatment of workers.

Read more: Bernie Sanders says Disney should use 'Avengers: Endgame' profits to hike workers' pay

As part of his 2020 platform, Sanders is calling for the federal minimum wage to be increased to $15 an hour and wants to make it easier for workers to join unions.

Critics of Sanders' plan contend raising the minimum wage would lead businesses to cut staff or raise prices.

The Vermont senator has introduced legislation that would gradually increase the minimum wage to $15 by 2024 to alleviate concerns about potential shifts in the market from an abrupt leap from the current federal minimum wage of $7.25 an hour.

As Uber prepares for its initial public offering (IPO), drivers in multiple cities — including New York City, Chicago, Los Angeles, and San Francisco — are striking on Wednesday. The strikes are also expected to extend to other regions of the world, including the United Kingdom and parts of South America.

The New York Taxi Workers Alliance (NYTWA), one of the organizations pushing for and organizing the strike, is calling for job security, livable incomes, and capping the companies' commission on rides to guarantee that 80% to 85% of the proceeds from a ride go to drivers.

Read more: Uber and Lyft drivers are striking in over a dozen cities around the world on Wednesday. Here's the full list of where demonstrations are planned.

"Wall Street investors are telling Uber and Lyft to cut down on driver income, stop incentives, and go faster to Driverless Cars," NYTWA executive director Bhairavi Desai said in a statement. "Uber and Lyft wrote in their S1 filings that they think they pay drivers too much already. With the IPO, Uber's corporate owners are set to make billions, all while drivers are left in poverty and go bankrupt. That's why NYTWA members are joining the international strike to stand up to Uber greed."

Companies like Uber and Lyft say their drivers are independent contractors rather than employees, which means they don't have to adhere to requirements on health care, minimum wage, or overtime.

A study from the Economic Policy Institute released Tuesday found Uber drivers earned the equivalent of $9.21 an hour "after accounting for Uber's commissions and fees and vehicle expenses, and taking into account the cost of a modest package of health insurance and other benefits equivalent to those earned by W-2 workers."

Read more: Uber and Lyft drivers are planning a massive strike this week over work conditions and pay rates

A separate recent study from Georgetown University's Kalmanovitz Initiative for Labor and the Working Poor, which is based off of a two-year investigation into the working conditions of 40 Uber drivers in Washington, DC, found 33% of drivers took on debt as a result of their work for the ride-hailing platform.