So far, 147 of its eligible 220 U.S. workers have signed cards with the Mapbox Workers Union.
The company, which provides mapping services and a location cloud platform for developers, did not immediately respond to a Reuters request for comment.
Its customers include Facebook Inc, Snap Inc, IBM Corp, Lonely Planet, CNN and Instacart.
Workers at technology firms like Google-parent Alphabet Inc and crowdfunding platform Kickstarter have formed unions to grapple with working conditions and business practices of big internet companies.
Meanwhile, e-commerce giant Amazon.com has resisted unionization fiercely.
San Francisco-based Mapbox is in talks with SVF Investment Corp 3 to take it public, according to a report by Sky News in April.