Amazon.com Inc.'s expansion plans, including its agreement to buy Whole Foods Market Inc. for $13.7 billion, are raising hackles in Washington — and Wall Street is taking notice.

A U.S. lawmaker has called for hearings on the proposed deal to consider its ramifications for shoppers and workers. Hedge-fund manager Doug Kass has taken a short position on the fast-growing online retailer, saying government antitrust concerns will erode its value. In June, Goldman Sachs issued a note questioning whether tech stocks are overpriced and whether investors have overlooked the risks associated with potential government regulatory issues.

Still, Amazon's shares have gained 34% this year, rising to $1,003.21 at 2:01 p.m. Friday in New York. Experts and analysts have largely dismissed antitrust threats for the world's largest online retailer because the company doesn't have large market concentration in any one product category and it has a track record of helping keep prices low for shoppers. A key legal question is whether Seattle-based Amazon has grown to the point of discouraging innovation from competitors.