From CNN Interactive Writer Marla Edwards

(CNN) -- If you're planning to fly with Northwest Airlines after August 29 on an important business trip, it would be wise to book a second flight as a backup, a consumer travel expert advised.

"If it's a trip you must take, it probably pays to just duplicate it somewhere else. If the trip is discretionary, if it's something that can be changed, it may pay to wait and see what happens," said Laurie Berger, editor of Consumer Reports Travel Letter.

Northwest pilots may strike as early as August 29, the deadline of a 30-day cooling off period that started when the National Mediation Board declared an impasse in talks between the airline and the pilots union.

The negotiations will resume Monday, said Marta Laughlin, a Northwest spokeswoman. "We are working hard toward reaching a negotiated settlement so there is no strike at all," she said.

A strike would be extremely disrupting, coming near the end of one of the busiest ever summers for air travel, said Ed Perkins, a consumer advocate with the American Society of Travel Agents (ASTA).

"It would effectively shut down about 11 percent of our nation's air passenger system," he said.

Northwest, which is the nation's fourth largest airline, is promising flyers that the airline will "make every effort" to accommodate flyers on another carrier at no additional charge or fully refund ticket prices.

"The last thing we want is to have a strike, and the first thing we need to do if that happens is take care of our customers as best we can, given the circumstances," Laughlin said.

Although airlines usually try to maintain goodwill among passengers by providing them with some compensation or a refund during a strike, there is no law that requires it, Perkins said.

"Since labor action falls into the same category as 'Act of God' and 'Act of War,' the carriers have no legal obligation to do anything for the consumer," he said. "There is a false perception out there that the airlines are required to compensate passengers when their flights are canceled or delayed, when in fact, they are only required to provide compensation to passengers who were bumped from an overbooked flight."

Other airlines routinely honor tickets from striking carriers as a courtesy, Berger said.

"The carriers get flooded with flyers from the striking carriers. They may not be able to accommodate everybody on the same flight that they originally booked or a similar flight. They may put you on a flight on a different day," she said.

She recommends that travelers do some research in advance to determine what other flights will be available if there is a strike. "Find a carrier with a similar schedule that flies to the same destination and ask how they would handle it."

Passengers should get a paper ticket if they have booked an electronic ticket, Perkins said.

"While many passengers have become accustomed to electronic tickets, they are still not easily transferable to other carriers in the event that your original airline isn't flying," he said.

Northwest has begun converting e-tickets to paper tickets for any flights booked directly with the airline for domestic travel August 28 through September 7 or international travel between August 26 and September 7.

Replacement paper tickets are being mailed to customers, and Northwest is communicating with travel agents to recommend they do the same for passengers they have booked. All future e-ticket requests for travel during the same period will be converted to paper tickets.

Both Berger and Perkins said flyers may find it easier to turn to their travel agents for help if there is a strike.

"Given the strong economy, and the high load factors, Northwest ticket holders could expect long and frustrating waits in finding alternate transportation if they don't have a travel agent," Perkins said.

Christine Levite, director of public affairs for American Express Co., advised ticket holders to keep up with the news about negotiations between the pilots union.

"It is really hard to say how other airlines might respond or how Northwest might respond. I think just being aware and learning about the alternatives through your travel agency is the best advice right now," she said. "We are not changing anyone's reservation, but we are getting prepared."

She warned that passengers in Northwest hub cities -- Minneapolis, St. Paul, Detroit and Memphis -- could have a particularly tough time finding other flights because there are fewer alternatives in those cities.

In those markets, more than 70 percent of flights are Northwest flights, Laughlin said.