Jones Day Reavis & Pogue is moving into the expanding Madrid market by merging with niche Spanish firm Tena Munoz y Asociados.
The firms will merge next year, a move which will upset local firms in the Spanish capital. Jones Day is the first US firm to fully merge with a Spanish practice.
The Lawyer revealed in May that Jones Day was looking to move into the Madrid and Milan markets.
A Spanish source says it is being viewed as the first real encroachment by US law firms.
Tena Munoz is a small commercial firm with five partners and one associate, specialising in securities work. Jones Day and Tena Munoz were unavailable for comment.