By Grant McCool

NEW YORK (Reuters) - Starbucks baristas were out of line sticking Industrial Workers of the World pins all over their clothing in support of attempts to be part of a labor union, a U.S. appeals court ruled on Thursday.

The court said a Starbucks Corp policy limiting employees to displaying only one pro-union button or pin on their work uniforms was not an unfair labor practice. One employee at a Starbucks location in New York had tried to display eight union pins on her clothing, according to court papers.

The case, a dispute between the National Labor Relations Board and the company, arose out of unionization efforts at several Starbucks coffee shops in Manhattan between 2004 and 2007. None of Starbucks's 7,000 stores in the United States are unionized.

Starbucks argued that a NLRB ruling allowing employees to wear an unlimited number of buttons would convert them into "personal message boards" for the union.

"We conclude that the Board has gone too far in invalidating Starbucks's one button limitation," the 2nd U.S. Circuit Court of Appeals said in its ruling. It said the company was entitled "to avoid the distraction" that numerous union buttons would create from messages on Starbucks-issued pins.

A spokeswoman for the NLRB declined to comment on the ruling.

Starbucks' one-button policy was carried out following an informal settlement with the NLRB in March 2006. The prohibited pins were less than 1 inch in diameter and bore the initials "IWW" for Industrial Workers of the World in white letters against a red background.

Starbucks spokesman Zach Hutson said the decision was an "affirmation of the progressive and positive workplace that we strive to create" for baristas and shift supervisors.

The case is the National Labor Relations Board v Starbucks Corp in the 2nd Circuit U.S. Court of Appeals No. 10-3511

(Reporting By Grant McCool; Editing by Martha Graybow, Tim Dobbyn and Carol Bishopric)