The European Commission claimed Microsoft had wished to retain the power of veto over which issues the trustee could examine. An EC spokesperson reportedly said: Their proposal on the monitoring trustee is not acceptable.

Any appointee would oversee Microsoft’s compliance with a series of remedies imposed by the EC under last year’s landmark antitrust ruling.

In that ruling, the EC ordered Microsoft to share Windows server APIs with competitors and to ship a version of Windows that does not contain Media Player, as compensation for abusing its dominant market position in servers and multimedia software.

The Commission also fined Microsoft 497.2m euros ($613m at the time, or $660m today).

This is the second time in less than a week Microsoft has landed in hot water with the commission over last year’s ruling.

Microsoft had proposed charging licensees of its server APIs up to $600 per server, however the Commission last week rejected this proposal saying it was too expensive. Competitors were also experiencing difficulty getting access to the information they needed to decide whether to buy a license, the EC said.

The EC can fine Microsoft up to five percent of its global sales for failing to comply with its original ruling, and regulators’ patience is clearly running out. A spokesperson said: The Commission remains patient, but there are limits to the patience.

Microsoft has 10 business days to respond to the latest ruling, after which time it will impose its own terms.