In 1968, Martin Luther King Jr. was assassinated after speaking with striking sanitation workers in Memphis.

In the decades since King’s murder, strike activity has fallen, but data from Cornell University shows that over the last two years it’s been picking up.

A lot of the big strikes last year were against big employers: Hollywood studios, major American automakers. But many were also against smaller employers, said Cathy Creighton at Cornell University.

“Restaurants, higher education, warehouse workers, a lot of teachers and public sector workers,” she said.

And those workers watched last year as the big strikes won big concessions from studios and automakers.

Jake Rosenfeld, a professor at Washington University in St. Louis, noted that those wins create momentum.

“We know from past research that successful strikes prove contagious. They tend to lead to other strikes,” he said.

Workers know that going on strike comes with the risk of job loss. But Rosenfeld said they also know they have options, considering how tight the labor market is right now.

“It grants them the freedom to take risks at work, such as participating in a strike, or threatening to unionize, without the fear that such activity could lead to a prolonged period of joblessness,” he said.

And as long as the unemployment rate stays low, Rosenfeld said strike activity will likely keep up.