BRUSSELS (Reuters) - Nippon Steel's ( NISTF ) $14.9 billion acquisition of U.S. Steel Corp will be decided by European Union antitrust regulators by May 17, with their approval a formality, a European Commission filing showed.

The Japanese steelmaker sought EU clearance on April 9, with the EC reviewing the deal under a simplified procedure, according to the filing.

Such a process is used for cases in which the EU competition enforcer has no competition concerns, or the companies' individual or combined market share is low.

Nippon Steel ( NISTF ), which clinched a deal to buy the 122-year-old American steelmaker for a hefty premium in December, however, faces headwinds with U.S. antitrust regulators.

Nippon Steel ( NISTF ) has manufacturing bases in Sweden, Finland and Britain and an office in Germany while U.S. Steel has a Slovakian subsidiary.