Amazon’s bid to acquire Whole Foods has sparked political concerns and prompted policymakers and legal experts to ask: How big is too big?

Amazon, America’s fifth largest Company by market value, is still growing like an adolescent and planting flags in new markets. That is prompting some policymakers and legal experts to ask: How big is too big?

It’s a key issue for an economy being rapidly reshaped by e-commerce, a sector where Amazon and the merchants operating on its platform account for up to a third of all U.S. sales, according to some estimates.

It’s also critical for Seattle, a city that has hitched its wagon to the e-commerce titan, and that once saw another local champion, Microsoft, mired in a lengthy antitrust battle. That fight, over Microsoft keeping a rival internet browser off PCs running Windows, almost led to the split-up of the Redmond software giant.

E-commerce is not Amazon’s only game. It also dominates cloud computing, and it may soon have a significant brick-and-mortar presence, with its pending acquisition of Whole Foods Market. The unexpected $13.7 billion deal announced in June spurred an outcry among critics of the company and some members of Congress who asked the Federal Trade Commission to take a close look at the deal.