When hurricanes, blizzards or other severe weather disrupt flights, some airlines are more accommodating than others in letting passengers rebook.

Tropical Storm Isaac is sweeping into the Gulf of Mexico and all the airlines with flights to and from the region this week are waiving their normal fees for passengers to rebook trips. So-called change fees can be as high as $150 on a domestic trip.

While it’s nice that airlines aren’t charging you to rebook, the time you have to take your trip depends on your carrier.

Some airlines are giving passengers nearly a year to fly while others are requiring passengers to be on planes as quickly as Friday.

“They are all over the place,” says George Hobica, founder of travel site AirfareWatchdog. He says the process should be standardized and that some of the airline requirements are harsh. “It’s not the passengers’ fault that a hurricane happened.”

The government doesn’t have rules for how much time airlines should give passengers to take their trip. The only protection passengers have is this: If their flight is canceled, the airlines must offer a refund.

Isaac, which could grow to a category 1 hurricane by late Tuesday night, has already led to more than 1,000 flight cancellations.

United Airlines and Frontier Airlines have the most generous policies. American Airlines, Delta Air Lines, JetBlue and US Airways have some of the most restrictive policies.

Dean Burri and his wife planned to fly American from their Florida home to the Bahamas for a one-night getaway this past weekend. The airline does offer a waiver for Florida passengers, but it doesn’t carry over until next weekend.

“I find American’s policy very cold-hearted, particularly in comparison to United’s very reasonable policy,” Burri says. “It’s certainly not consumer friendly.”

• United is offering passengers flying into affected cities three options. They can get a full refund whether or not their flight was cancelled. They can rebook on flights anytime within a year of the day they purchased their ticket and avoid a change fee – but will have to pay for any difference in price. They can rebook onto a flight by this weekend and avoid any change fee and fare differences.

• Frontier is letting those passengers who aren’t already traveling move to a flight within its currently published schedule, which goes through March 17.

• American is telling passengers with tickets to eastern Florida that they must fly by Wednesday; Key West or western Florida by Friday and the Gulf Coast by Sunday.

• Delta is requiring travelers to or from Florida to start their revised plans by Friday and those to or from the Gulf Coast by Sunday.

• JetBlue is requiring Florida passengers to fly by Friday.

• US Airways also has Florida fliers traveling by Friday and those in the Gulf by Saturday.

• Virgin America is giving a bit more leeway, allowing trips to start by Sept. 4.

• Spirit Airlines is requiring all travel to be completed by Sept. 27.

• Southwest Airlines is requiring passengers to start their new trips within 14 days of the original date of travel. The airline doesn’t charge change fees but requires passengers to pay for a difference in fare.

Even in natural disasters, airlines are doing what’s best for their bottom line, not their customers, says Charlie Leocha, director of the Consumer Travel Alliance who sits on the Department of Transportation’s Advisory Committee on Aviation Consumer Protections.

“The airlines are doing things to make money. I think they’ve given up the whole concept of being fair,” says Leocha.

Each airline has its change requirements posted on their website.