A Monday deadline loomed for pilots at

Delta

(DAL) - Get Delta Air Lines, Inc. Report

and

Northwest

(NWA)

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to approve a joint collective bargaining agreement ahead of the airlines' proposed merger later this year.

The agreement would be an important step for the proposed combination of the two companies. While the unions cannot stop the deal from happening, agreement among the more than 12,000 pilots it would represent a major boost to workplace harmony following it. The two pilot groups, represented by the Air Line Pilots Association, came to a

tentative agreement

in June.

Delta and Northwest plan to close the deal, which still requires shareholder and U.S. regulatory approval, later this year.

This article was written by a staff member of TheStreet.com.