Last month Illumina defended its case before senior European Commission and national competition officials at a closed hearing but failed to convince them, the people said.

Illumina, which last year set aside $453 million for a potential EU fine, said it would appeal against any fine.

"We disagree that the Commission has jurisdiction to review the GRAIL transaction as well as with the premise of the Commission imposing a fine," it said in an emailed statement.

"We have appealed the EU's jurisdiction and will appeal any decision imposing a fine. Illumina's merger with GRAIL is pro-competitive and in the best interests of patients in Europe and worldwide," the company added.

The European Commission has in recent years taken a tough line against companies which fail to notify their mergers or standstill obligations during regulatory scrutiny of the deals.

Illumina angered the European Union competition enforcer when it completed the acquisition of U.S.-based biotechnology company Grail in August 2021 amid an ongoing EU investigation.

The Commission, which last year blocked the Grail deal, declined to comment. It is expected to impose the fine on Illumina in the coming months, the sources said.

Illumina has already challenged the EU's veto, the EU decision to examine the case despite the deal not meeting the EU turnover threshold for scrutiny and the EU order to keep Grail separate so that it can unwind the takeover.

(Reporting by Foo Yun Chee; Editing by Alexander Smith)

By Foo Yun Chee