The UK computer agency Becta is advising schools not to sign licensing agreements with Microsoft because of alleged anti-competitive practices.
The government agency has complained to the Office of Fair Trading.
It says talks with Microsoft have not resolved "fundamental concerns" about academic licensing and about Office 2007 and the Vista operating system.
Microsoft says it wants as many people as possible to benefit from its technology at the best possible price.
Information and communication technology (ICT) is an essential subject in schools, which have to spend huge sums on installing, upgrading and maintaining equipment and software.
Microsoft, Windows Vista, Microsoft Office 2007, Becta, Deal