(Reuters) -Amazon Web Services CEO Adam Selipsky will step down, handing over the reins of the retail giant's crucial cloud business to long-time insider Matt Garman, the company said on Tuesday.

Senior Vice President Matt Garman will take on Selipsky's role at AWS, effective June 3, the firm said.

The move comes at a crucial time for the cloud business that brings in much of Amazon's ( AMZN ) profit.

While it has the largest share in the U.S. cloud market, its dominance is under pressure from Microsoft's fast-growing Azure service that is benefiting from AI offerings powered by its tie-up with OpenAI.

AWS, its second-biggest business unit after e-commerce, is widely regarded as Amazon's ( AMZN ) growth engine, contributing about 40% to the company's top line.

Garman started at Amazon ( AMZN ) as an intern during the summer of 2005 and joined the company full-time the next year as one of its first product managers.

Selipsky has spent 14 years at AWS over two stints. He was the CEO of Tableau Software, a unit of Salesforce, from 2016 to 2021.