eBay said its rival, Amazon, supports the act.
Online retailer eBay has called online marketplace sellers to help lobby against US sales tax legislation, which the company says will burden small online merchants.
eBay chief executive John Donahoe told Reuters the company will send out millions of e-mails to users asking them to send a messages to members of the US Congress to request changes to the Marketplace Fairness Act.
Reuters reported that the legislation, which is scheduled to be voted on by the Senate in coming days and gives states the power to compel retailers outside their borders to collect online sales tax.
Donahoe said that eBay’s chief rival, Amazon, supports the legislation.
"This legislation treats you and big multi-billion dollar online retailers – such as Amazon – exactly the same," Donahoe said.
"Those fighting for this change refuse to acknowledge that the burden on businesses like yours is far greater than for a big national retailer."
eBay has reported a 14% increase in its first quarter revenue to $3.74bn, compared to $3.27bn it reported for the corresponding period of 2012.
The company’s net income rose 19% to $677m, or $0.51 diluted earnings per share, for the quarter, compared to $570m, or $0.44 diluted earnings per share, for the same period last year.