EU officials yesterday also ordered Google to stop using its popular Android mobile operating system to block its rivals, adding to trade tensions between Washington and Brussels.
European Commission President Jean-Claude Juncker is scheduled to meet with Trump at the White House next Wednesday to discuss trade and other issues.
But ahead of the meeting Mr Trump fired an angry warning shot at Brussels.
The US president referenced the ongoing trade war with the bloc and said he saw the Google fine as an attack on America.
He tweeted: “I told you so! The European Union just slapped a Five Billion Dollar fine on one of our great companies, Google.
“They truly have taken advantage of the U.S., but not for long!”
Google said it would appeal the EU decision.
The 4.34 billion euro (£4.2billion) fine is nearly double the previous penalty that the company was ordered to pay last year, but it represents a little more than two weeks of revenue for its parent company, Alphabet Inc.
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The penalty was announced at a press conference in Brussels yesterday. The fine is the largest imposed by the bloc on one single firm.
Explaining the fine, EU competition commissioner Margrethe Vestager said yesterday: “Our case is about three types of restrictions that Google has imposed on Android device manufacturers and network operators to ensure that traffic on Android devices goes to the Google search engine.
“In this way, Google has used Android as a vehicle to cement the dominance of its search engine. These practices have denied rivals the chance to innovate and compete on the merits.
“They have denied European consumers the benefits of effective competition in the important mobile sphere. This is illegal under EU antitrust rules.”
Mr Juncker is due to meet the US president in Washington next week.
The pair are expected to discuss the ongoing trade war which has seen a series of tit-for-tat tariffs slapped on the EU and US.
And it comes after Mr Trump last week described Brussels as “a foe”. He has constantly referred to the EU being “very unfair” on trade and pointed out the US has a vast trade deficit in relation to Brussels nations.
Despite the ongoing tensions, Mr Juncker insisted he was “upbeat and relaxed” ahead of his US trip.
The EU President said: “When it comes to trade, the European Union, its internal market, its single market, form an indivisible unity and it’s the Commission that is in charge of articulating trade policy. All efforts to divide the European Union are in vain.”