Northwest wants to cut $2.5 billion in costs, including $1.4 billion annually in labor costs.
Doug Steenland, the airline's president and chief executive officer, called the filing in New York bankruptcy court a "backstop" to negotiations for consensual cuts.
The airline outlined new targets for union concessions in the filing, and said salaried and management employees would also take a second round of pay and benefit cuts soon.
Northwest previously announced plans to reduce its flight schedule, and the airline expanded on that in the filing, describing it as "right-sizing the airline."
Northwest expects fourth-quarter mainline capacity to be cut 7 to 8 percent from the period a year ago, with domestic flights cut more sharply than overseas routes. More schedule reductions are planned starting in January, tentatively 11 to 13 percent of capacity compared to a year earlier.
The schedule may eventually be cut as much as 15 percent or more, Northwest said.