Sun Microsystems developed the Java programming language
The European Union (EU) has launched a probe into the $7.4bn (£4.5bn) takeover of computer maker Sun Microsystems by business software firm Oracle.
The EU is concerned that the deal, if approved, could breach competition rules, leading to higher prices and less choice for customers.
Last month, the US Justice Department gave its approval to the deal, agreed between the two firms in April.
The EU said it would make its final decision by 19 January.
EU Competition Commissioner Neelie Kroes said the union was obliged to investigate "when the world's biggest proprietary database company proposes to take over the world's leading open-source database company".
The acquisition is important to Oracle, because it would give the company control over Java, a key programming language used in billions of electronic devices across the world.
The takeover has already been held up over questions about licensing Java.
The deal was expected to be finalised at the end of the summer.
Oracle is looking to strengthen its position against rival IBM, which abandoned its own attempts to buy Sun earlier this year.