ATLANTA (Reuters) - The National Labor Relations Board said on Friday it dismissed a high-profile case that accused Boeing Co of illegally opening a non-union production line in South Carolina to punish unionized Washington-based workers for past labor strikes.

The complaint, originally lodged by the International Association of Machinists and Aerospace Workers union, said Boeing engaged in unfair labor practices by locating a second assembly line for the 787 Dreamliner in the southern U.S. state.

"The union asked to withdraw the charge following the ratification of a four-year collective bargaining agreement between its members and Boeing earlier this week," NLRB Acting General Counsel Lafe Solomon said in a telephone briefing with reporters.

The contract extension, approved this week, ensures the upcoming version of Boeing's best-selling 737 narrowbody aircraft, called the 737 MAX, would be built in Washington state, where Boeing has always made its jets.

Boeing shares were up 1.9 percent at $71.51 in afternoon trading.

(Reporting by Karen Jacobs in Atlanta; Editing by Andre Grenon)