Microsoft has asked US federal courts to force four of its rivals to hand over documents relating to its fight against European Commission sanctions.
Microsoft's dominant position has brought a number of complaints
The software giant is demanding the papers from IBM, Sun Microsystems, Oracle and Novell.
Microsoft could face anti-trust fines of up to 2m euros ($2.4m; £1.4m) a day if found to be dragging its heels over a 2004 EU court ruling.
The court ordered the firm to open up its software code to rivals.
The ruling had fined Microsoft 497m euros for abusing its dominant market position.
Last month Microsoft's rivals accused it of delaying tactics over the matter and filed a fresh complaint with Brussels.
Microsoft said on Friday that it had asked the European Commission for the documents in question, but as they had not all been forthcoming, it was now trying to force its competitors through the US courts.
It added that it needed the documents to help its defence.