President Barack Obama supports the bill, but its fate is uncertain in the House, where some Republicans regard it as a tax increase.
The bill pits brick-and-mortar stores like Wal-Mart against online services such as Ebay. The National Governors Association and the National Retail federation support it.
Amazon.com, which initially fought efforts in some states to make it collect sales taxes, supports the bill.
“Amazon.com has long supported a simplified nationwide approach that is evenhandedly applied and applicable to all but the smallest volume sellers,” Paul Misener, Amazon’s vice president of global public policy said in a recent letter to senators.
Ebay has been rallying customers to oppose the bill.
“I hope you agree that imposing unnecessary tax burdens on small online businesses is a bad idea,” eBay president and CEO John Donahoe said in a letter to customers. “Join us in letting your Members of Congress know they should protect small online businesses, not potentially put them out of business.”
The bill is also opposed by senators from states that have no sales tax, including Sen. Max Baucus, D-Mont., and Sen. Kelly Ayotte, R-N.H.
“Supporters of this online sales tax bill are trying to muscle it through before senators find out how disastrous it would be for businesses in their states,” Ayotte said. “I will fight this power grab every step of the way to protect small online businesses in New Hampshire and across the nation.”