A measure that would empower US states to require out-of-state retailers to collect online sales tax won backing from President Barack Obama on Monday and is expected to pass a legislative test vote in the Senate later this evening. 

The bill will be the subject of a procedural motion that, if approved, will clear the way for a final vote in the Democratic-controlled Senate, likely on Wednesday. 

Supporters of the measure include brick-and-mortar retailers such as Wal-Mart Stores Inc and Best Buy Co Inc and cash-strapped state governments, along with Amazon.com Inc , which hopes to simplify its US state retail tax situation. Opponents include many online merchants, including eBay Inc and Overstock.com Inc. 

Congressional backers say they have the 60 votes needed to end debate in the Senate. Momentum has been building since 75 of 100 senators last month voted for a non-binding version of the bill. 

Prospects for the bipartisan measure are murkier in the Republican-controlled House of Representatives, where some Republicans view it as a tax hike. 

Lobbyists on both sides are working to make their case in Congress, with several new wrinkles emerging on Monday, a key one being that the Obama administration for the first time officially backed the measure. 

White House spokesman Jay Carney said the bill "will level the playing field for local small business retailers who are undercut every day by out-of-state on-line companies." 

Amazon, with its extensive network of distribution centers, already collects tax in nine states, and has agreements with seven more states to start charging in the next year. Amazon has been actively supporting the bill on Capitol Hill. 

The bipartisan National Governors Association supports the tax, and in a letter to lawmakers on Monday said the disparate treatment of online and Main Street businesses is "shuttering stores and undermining state budgets." (Economic Times)