Retailers are not happy about Amazon's recent promotion giving customers up to $5 off purchases when they use the company's app to compare in-store prices with the online retailer. And now congress is weighing in, according toThe Hill.

U.S. Sen. Olympia Snowe (R-Maine) called the incentive "an attack on Main Street businesses that employ workers in our communities," and wants Amazon to cancel the program.

"Small businesses are fighting every day to compete with giant retailers, such as Amazon, and incentivizing consumers to spy on local shops is a bridge too far," she said in a statement.

Snowe's criticism comes while Congress is also debating a national online sales tax promising to have broad impacts on the online retail industry in general and e-commerce giant Amazon in particular.

Amazon also is in hot water with U.S. Rep. Ed Markey (D-Mass.) who has raised privacy concerns about Amazon's Kindle Fire, claiming its browser could give Amazon unique insight into the Web clicks, buying patterns and media habits of Fire users with browser data from Amazon servers.

Markey has asked Amazon to reveal more details about the browser.

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