The co-chairwoman of Morgan, Lewis & Bockius’ labor and employment practice has left the Philadelphia-based firm for the New York office of Jones Day.

Doreen S. Davis, a traditional labor law attorney who focuses on matters related to collective bargaining and union organizing, not only co-led Morgan Lewis’ work in that area but also served as head of the labor and employment group in Pennsylvania.

Friday was Davis’ last day at Morgan Lewis and she begins her work at Jones Day today.

The longtime Pennsylvania resident isn’t giving up her roots in the Keystone State. She has rented an apartment in New York and will stay there during the week while maintaining her Haverford, Pa., home. Davis said Jones Day has no plans of opening a Philadelphia office.

Davis said she is good friends with the head of Jones Day’s New York office, partner Willis J. Goldsmith, who also happens to head the labor law practice at Jones Day.

“Doreen is an outstanding addition to our labor and employment practice,” Larry DiNardo, head of Jones Day’s labor and employment practice, said in a statement. “Her deep background on NLRB and union matters brings additional depth to our already very significant labor and industrial relations capabilities, and our union organizing, and collective bargaining experience, areas of critical concern to many employers and capabilities where Jones Day has a rich tradition serving our clients.”

Davis said her new firm had been looking for some time for a senior lawyer who focused solely on traditional labor law. She said Morgan Lewis is a great firm and she has had “a fabulous time” working there, but said she was very excited for the opportunity to work in New York.

“They are a larger platform than Morgan,” Davis said of Jones Day. “[Jones Day has] an excellent labor and employment group who we always considered at Morgan to be our bigger competitor.”

Morgan Lewis has often won awards, including one recently from The Legal, for its prominent labor and employment practice. Davis said Jones Day’s practice handles similar matters. She said some of Jones Day’s clients include Verizon and IBM. Davis said she was one of a few people at Morgan Lewis who focused solely on traditional labor law.

She said Jones Day might not have as many attorneys focusing on that type of work as Morgan Lewis did. But Davis pointed out Jones Day is a larger platform, with more than 2,400 lawyers compared to Morgan Lewis’ 1,300 attorneys.

Morgan Lewis has higher revenue per lawyer (RPL) and profits per equity partner (PPP) than Jones Day. Morgan Lewis’ RPL is $895,000 compared to Jones Day’s $685,000. Morgan Lewis’ PPP is $1.5 million while Jones Day’s PPP is $870,000. Jones Day brought in $1.65 billion in gross revenue in 2011 while Morgan Lewis earned $1.16 billion.

Joe Costello, head of Morgan Lewis’ labor and employment practice firmwide, said Davis was a very important contributor to the Philadelphia office and the firm’s labor practice. Costello said the firm wishes Davis well, but said it wouldn’t miss a beat because it has labor lawyers across its offices in Philadelphia, Chicago, Los Angeles, Washington, New York and Houston.

“This is really a win-win,” Costello said. “Doreen will have a chance to fulfill her dream of practicing in New York and we’ll use this as an opportunity to bring new leadership to our traditional labor practice.”

To that end, John Ring in Washington and Joseph C. Ragaglia in Philadelphia will now co-lead the labor practice at Morgan Lewis, Costello said.

Davis said her clients would be following her to Jones Day.

Davis has spent the last 11 years at Morgan Lewis and before that spent an equal amount of time at Montgomery McCracken Walker & Rhoads, where she led that firm’s labor and employment group. Shortly before leaving Montgomery McCracken, Davis served in 2000 as chancellor of the Philadelphia Bar Association.

Davis has a national practice concentrated on National Labor Relations Board matters related to litigation, union organizational activities and collective bargaining. She advises clients on the labor implications of mergers and plant consolidations and has served as defense counsel in nationwide class actions and charges by the Equal Employment Opportunity Commission related to sex-discrimination claims brought under the Fair Labor Standards Act. Davis began her career as a field attorney with the NLRB’s fourth region, which encompasses Philadelphia.

Sandra Mannix of Abelson Legal Search said Davis has been such an important part of the Philadelphia legal community for so long that it is difficult to believe she will be working outside of the city.

“You just think certain people will be here forever,” Mannix said.

Mannix said Davis has long had a truly national reputation in her practice area.

“If someone asked you to name the top labor and employment lawyers in Philadelphia, I can’t think of anyone who wouldn’t put her in the top three,” Mannix said. “She has that kind of a reputation.”

Gina Passarella can be contacted at 215-557-2494 or at gpassarella@alm.com. Follow her on Twitter @GPassarellaTLI.