An activist investor wants Peloton Interactive Inc. to fire its chief executive and explore a sale after the stationary-bike maker’s stock plummeted more than 80% from its high, as growth slowed.

Blackwells Capital LLC has a significant stake of less than 5% in Peloton and is preparing to push the company’s board to fire CEO John Foley and pursue a sale, according to people familiar with the matter. The firm believes Peloton could be an attractive acquisition target for larger technology or fitness-oriented companies, the people said.