What does it mean to hold a job nowadays?

It’s estimated that by 2020 more than 40% of U.S. labor will be freelance or contract workers. Data from research group Economic Modeling shows the share of traditional, 9-to-5 workers in the labor force has been dropping steadily for more than a decade.

That growth in freelancers and the related rise of the Internet-enabled “gig economy” challenge long-held ideas of what defines a career. It’s also leading to important questions about the future of the U.S. labor market and prompting everyone to ask what, if any, obligations businesses should have toward their contractors.

This came to a head this past summer when the California Labor Commission ruled that an Uber driver was an actual employee, not a contractor. Still, that was just one person. Several weeks later, a federal judge allowed Uber drivers to move forward with a class-action lawsuit to be designated employees. (Uber has been singled out as a particularly egregious case: of the 160,000 people who work for the company, only 4,000 are considered employees.) If the class-action succeeds, business professor Arun Sundararajan argued in the Financial Times, “Start-ups that rely on a large pool of smartphone-toting casuals working irregular hours may find that their business models are no longer viable.”

Contractors may have more flexibility in how and when they work (though not always), but they are denied the benefits and protections full-time employeesreceive, including retirement plan contributions, health or disability insurance, sick pay, and half of Social Security/Medicare taxes. They aren’t subject to minimum wage or overtime rules either. That disparity led Los Angeles Times business columnist Michael Hiltzik to write that sharing-economy startups like Uber “have always been based on something of a sham.”

Is it time to disentangle benefits from the job contract? Venture capitalist Nick Hanauer and labor leader David Rolf argue it is. Writing in Democracy Journal, they say this shift away from full-time work creates such economic uncertainty for those hustling together multiple gigs that it “threatens to undermine the very foundation upon which middle-class America was built.” If micro-employment is the future, then we need a mandatory benefits package that is pro-rated (for part-time workers), portable, and accrues benefits (retirement, vacation days) over time. “A robust set of mandatory universal benefits would put all employees and employers alike on an equal footing, while providing the economic security and certainty necessary for the middle class to thrive,” they write.

On-demand companies, such as Lyft and Instacart, are listening. Just this week, the two formed a coalition with labor groups to advocate protections and benefits for independently contracted workers.