Seattle’s city council will vote on a landmark bill Monday that could help Uber and Lyft drivers unionize.

If passed, the measure would give those paid to drive passengers—which includes taxis, for-hire companies, and ride-sharing apps like Uber and Lyft—the opportunity to collectively negotiate compensation and working conditions.

The bill, one of the first of its kind, also acknowledges the status of Uber and Lyft as independent contractors and would help them bypass the National Labor Relations Act. As it stands, the act doesn’t protect the right of such contractors to bargain directly with the companies employing them.

Additionally, the legislation would certify non-profit organizations that represent drivers who have a for-hire vehicle and have met a minimum threshold of trips in Seattle. This would then give them bargaining power with Uber and could cost the company around $4.1 billion more on expenses associated with hiring full-time employees.

Seattle is not the only battleground in the debate over how to classify drivers with Uber and Lyft, who have stringently opposed labeling their drivers as full-time employees. Uber is currently involved in a class-action lawsuit over this issue in California, and in June, the California Labor Commissioner’s Office ruled that a former driver for Uber should have been classified as an employee.

Other states, such as Ohio and Florida, are moving ahead with regulations that would designate drivers for ride-sharing companies as independent contractors.

Both Uber and Lyft have said drivers prefer the option of flexibility when working for on-demand companies. “Uber is creating new opportunities for many people to earn a better living on their own time and their own terms,” according to Uber in a statement to Fortune. “Drivers say that with flexible and independent work with Uber, 50% of them drive fewer than 10 hours a week, 70% have full-time or part-time work outside of Uber and 65% choose to vary the hours they drive 25% week-to-week.

Lyft said in a statement to Fortune that the proposed legislation “raises a range of concerns, including violating Seattle drivers’ privacy rights and circumventing federal laws.”