On Sunday, Reuters reported that millions of eBay users woke up to an e-mail from Chief Executive John Donahoe. Donahoe reached out to argue against pending federal sales tax legislation in the Senate, encouraging merchants to lobby their representatives quickly.

The Marketplace Fairness Act is set to be voted upon within the next several days. It empowers states to compel retailers outside their borders to collect sales tax for online purchases. In other words, an Illinois retailer shipping to a Californian would now be required to collect California sales tax then send that money back to the Golden State. At present, states can only require this of companies that have an in-state physical presence.

However, there is currently an exemption for retailers that make less than $1 million in out-of-state revenue—but Donahoe pushed for this limit to be raised to $10 million, or for the exemption to cover companies with less than 50 employees.

"This legislation treats you and big multi-billion dollar online retailers—such as Amazon—exactly the same," Donahoe wrote. "Those fighting for this change refuse to acknowledge that the burden on businesses like yours is far greater than for a big national retailer."

The legislation is supported by a long list of companies and politicians: Amazon, Barnes & Noble, Best Buy, Gap, Wal-Mart, and 29 bi-partisan state governors. Notable opponents include eBay, the Heritage Foundation, and Americans for Tax Reform among others.