BRUSSELS — Europe’s antitrust regulators are preparing to deliver a strong message: a deal is a deal, and if a company fails to live up to a settlement agreement, there will be consequences.

On Wednesday, the European Union is expected to impose a large fine on Microsoft for failing to give users of the company’s Windows software a choice of Internet browsers. It would be the first time that European regulators had punished a company for neglecting to comply with the terms of an antitrust settlement, and it could signal a tougher approach to enforcing deals in other antitrust cases, including one involving Google.

Microsoft and officials at the European Commission reached an antitrust settlement in 2009 that called on the company to give Windows users in Europe a choice of Web browsers instead of pushing them to Microsoft’s Internet Explorer. But Microsoft failed to offer users such a choice for more than a year — apparently without anyone at the company or the commission noticing.

Last July, the company admitted the problem and apologized. It said the failure was a result of a technical issue that had escaped its notice, and it updated its Windows 7 and Windows 8 software to give European users the browser choice.