Oracle is marshalling select customers in Brussels for its two-day meeting with European commissioners to persuade them to give its proposed acquisition of Sun Microsystems the go-ahead.
The European Commission has delayed approval of the $7.4bn deal, even though US authorities have given it the green light.
European competition authorities are concerned that the combination of Sun's MySQL database product and Oracle's products could harm competition.
A number of big corporate and government technology users are set to appear at the hearing in Brussels to back Oracle, according to the Financial Times.
Oracle insists that its planned acquisition of Sun Microsystems will not harm competition in the database software market because there is no overlap between the two products.
Oracle supporters are said to include Ericsson, Vodafone, Sabre and the UK's Atomic Weapons Agency and National Health Service.
Even rival IBM has said that the deal will not raise any significant anti-trust issues because it is not the most sophisticated database in the marketplace and there are plenty of alternatives.
But critics say that acquiring MySQL will put Oracle in a position to stifle the business.
The most common competitor to MySQL is Oracle, according to Monty Widenius, the founder of the MySQL, who sold out to Sun in 2008 for $1bn.
Widenius is set to appear at the Brussels hearing to back the Commission's case, along with Oracle rivals SAP and Microsoft.
Oracle has called Marten Mickos, a former chief executive officer of MySQL, and Eben Moglen, a professor at Columbia Law School and founder of the Software Freedom Law Center, to support its argument.
European competition authorities have recently expressed optimism about reaching a settlement with Oracle.
If the hearings fail to resolve the issue, European authorities have until 27 January to make a final decision on whether or not to allow the deal to go ahead.