A German bank staff union on Thursday called on Berlin to prevent UniCredit from buying Commerzbank , warning of massive job losses if the deal goes through.

Another person with direct knowledge of the matter said UniCredit’s “assault” on Commerzbank was perceived in Berlin as an “unfriendly act.” The person added it was “nonsensical” for UniCredit’s chief executive Andrea Orcel to argue the German government welcomed his bid.

UniCredit was able to buy 4.5% of Commerzbank from the German state because the government trusts the Italian bank, its CEO said in a newspaper interview, ruling out any "aggressive" moves such as an unsolicited buyout bid.

Analysts have welcomed the move by UniCredit, particularly because a tie-up between the two banks might spur more M&A activity in Europe's banking sector.