Twilio CEO Jeff Lawson blamed Uber for the software developer's disappointing financial results.
Uber accounts for 12 percent of Twilio's revenue. Uber uses the company's software to connect drivers and passengers without divulging personal information.
Lawson said on Tuesday that he expects Uber's "contribution to decline" because the ride-hailing company is "changing the way they do
Uber and Facebook's WhatsApp are Twilio's two biggest customers. Not including Uber, Twilio's base revenue jumped 60 percent in the first quarter.
Lawson's comments suggest that Uber is taking over its messaging and doing more internally.
"There are very few companies in the world with the global scale and engineering prowess to take on a project of this magnitude," Lawson said. The changes "will restrain overall growth in 2017," he said.
Twilio shares plunged 30 percent in extended trading after the company gave a revenue forecast for the second quarter and full year that trailed analysts' estimates.