Microsoft yesterday accused the EC (European Commission) of actively working with the company's rivals and failing to act as an independent regulator in its ongoing antitrust case against the software giant.

In an additional response to the EC's statement of objections – a recent set of arguments explaining why it believes the company has failed to comply with its 2004 antitrust ruling – Microsoft says the EC encouraged "secret contacts" between the company's rivals, the independent trustee meant to monitor compliance with the case and internal technical experts.

The company says encouraging these contacts "violated fundamental principles of due process" and represented "direct violations of procedural safeguards aimed at ensuring transparency of the monitoring process".

As part of monitoring compliance with the EC's 2004 antitrust decision, which ordered the company to ensure interoperability for its workgroup server software, among other rulings, the EC selected an independent monitoring trustee, computer science professor Neil Barrett, from a list proposed by Microsoft. The EC is the EU's (European Union's) executive branch and regulatory authority.

But Microsoft argues that the EC encouraged a series of contacts among the company's rivals, including Sun Microsystems and IBM, the trustee and EU technical experts. These contacts were part of an attempt by the EC to "educate" the trustee "in a manner detrimental to Microsoft", the document says.

It also alleges that the statement of objections, rather than being an "independent, impartial assessment" of the technology-interoperability information Microsoft has supplied in the case, were "argumentative tracts" developed for the EC with the help of the company's rivals.

This behaviour, the document claims, suggested that the EC, the trustee and Microsoft's rivals were collaborating in a manner "inconsistent" with the EC's role as "neutral regulator" and the trustee's role as "independent monitor".

An EC spokesman confirmed that body had received a "supplementary response" to the statement of objections it sent to Microsoft on 21 December, but declined to immediately comment on the content of the company's document.

Jonathan Todd, spokesman for EU Competition Commissioner Neelie Kroes, said the EC's statement of objections was supported by two reports from the independent monitoring trustee.

Todd said the statement of objections reflected the EC's initial view that Microsoft had not yet provided "complete and accurate specifications for [the] interoperability information" that the antitrust ruling required. He also confirmed that hearings for Microsoft to present counterarguments would be held on 30 and 31 March.

Todd added that the EC would decide whether to impose fines, of up to €2m (about £1.37m) a day, after the hearings take place. The fines would be imposed if the EC decides that Microsoft has not taken steps required by the antitrust ruling. These steps include publishing the information necessary to allow products from Microsoft rivals to interoperate with Microsoft software.