
The move is part of Microsoft's progression to Office 2007, which was launched for business customers through Volume Licensing in November 2006 and went to general availability through retailers and OEMs in January 2007.
Although Microsoft will stop shipping the software, the company said that some authorised distributors may have remaining stock for a time.
Eric Ligman, senior manager for small business community engagement at Microsoft, warned of the potential for pirates to attempt to capitalise on the announcement.
"Microsoft system builders should make sure that they are buying legitimate Microsoft OEM software through authorised distributors to help protect clients from illegal or counterfeit software floating around," he said in a blog posting.
"I have posted a list of OEM System Builder Partner Resources and posted about the dangers of buying OEM through sites online in the past. Not to mention the potential exposure to an audit or fine that illegal software opens your clients up to."
Ligman also pointed out that, by taking advantage of the downgrade rights included in the Volume Licensing versions of Microsoft Office 2007, clients can move to Office 2007 when they are ready without having to re-buy their Office licence like they would with an OEM.
Mainstream support for Office 2003 will continue until 13 January 2009. Extended support, including security updates and pay-by-incident support, will cease on 14 January 2014.