The commission is delaying approval of the deal because of concerns that the combination of Sun's MySQL database product and Oracle's products could harm competition.
But the UKOUG, an independent, not-for-profit organisation with more than 10,000 members, said MySQL is not the main issue.
Providing a determined future for Java and for those members with a significant investment in Sun hardware is of vital importance, the group said.
For this reason, the UKOUG said the acquisition should be allowed to go ahead without further delay.
"Uncertainty over the future of Java risks our members' investments in both Oracle technologies and in developed applications," said Ronan Miles, chairman of the UKOUG.
"In terms of strategy and commitment to open source, Oracle will provide a secure future for Java.
"Oracle's record of preserving customer investments and support of open standards would indicate as safe future for MySQL as any other 'owner'."
Oracle has also demonstrated how it is able to absorb the people from acquired companies to drive the best product development - and hence best customer value, said Miles.
Oracle is to meet European Union regulators on 10 December in an attempt to win approval for the acquisition of Sun Microsystems
European competition commissioner Neelie Kroes said earlier this month she believed it was still possible to reach a settlement with Oracle.
"Let's be optimistic, and let's find out if they could take us to a point that we say, 'Okay, here we can take the result as a satisfying result for fair competition'," she told journalists.
The EC began an investigation into the acquisition in September after lobbying by Oracle rivals. It is scheduled to make a ruling by 27 January 2010.
If Oracle fails to satisfy EU regulators at the coming meeting, the enterprise software supplier can appeal to the European courts in Luxembourg.