Delta Air Lines, Inc. (DAL - Free Report) on Monday lowered its performance estimates for the first half of 2017, and now its stock is down 3.41% to $48.40 per share through early afternoon trading. Stocks of other big U.S. airlines have also experienced some turbulence on the back of the Delta news, high oil prices, and fallout from President Donald Trump’s travel ban.

Southwest Airlines Co. (LUV - Free Report) stock is down 2.36% to $57.46 per share in Monday trading. American Airlines Group, Inc. (AAL - Free Report) stock is down 4.46% to $44.73 per share. United Continental Holdings, Inc. (UAL - Free Report) stock is down 4.18% to $72.46 per share. And US Global Jets ETF (JETS - Free Report) stock is down 2.08% to $28.71 per share.

Delta’s 8-K filing identified both lower unit revenue and higher costs as reasons for its lowered first half of 2017 expectations. The Atlanta-based airline predicted its Revenue per Available Seat Mile or unit revenue, which is calculated by dividing an airline’s total revenue by its total available seat miles, will be flat in the first quarter of 2017. This came after Delta predicted in January its unit revenue would increase by 2%.

Rising oil prices also contributed to Delta’s lowered expectations. "Market fuel prices are tracking up about 55% for the quarter, which is expected to be the greatest year-on-year increase in 2017," the filing noted.

This downturn comes only a few weeks after Warren Buffett’s Berkshire Hathaway Inc. bought an eye-popping 43.2 million shares of Southwest Airlines in the fourth quarter.

Berkshire’s new position in the low-cost carrier is valued at $2.2 billion. Buffett’s company also invested heavily in American Airlines, Delta and United, which signaled a shift in Buffett’s decades-long stance that airlines were money-losers.

Updated Travel Ban

Trump and the White House announced Monday morning an updated, less-drastic version of its travel ban. The new executive order removed Iraq from the list, leaving Iran, Libya, Somalia, Sudan, Syria and Yemen. Iraq was removed after political pressure mounted, a great deal of which hung on the continuation of a joint U.S. and Iraqi effort to fight the Islamic State.

The revamped executive order now exempts travelers holding valid visas or green cards as of Jan. 27, the date the initial ban went into effect. The new order also treats Syrian refugees, which were banned outright in the first order, the same as those from other countries.

Trump’s updated travel ban will not be put into action until March 16. The delay was implemented in order to address potential legal concerns.

The new travel ban also comes after reports showed that the number of people visiting the U.S. from foreign countries has decreased significantly. New York City could see foreign travel decrease by over 2% in 2017, which would be the first drop in eight years. Other major U.S. cities have predicted a similar drop.

A decrease in International travel could create $7.4 billion in lost revenue.

Airline Update: More Economy Flights

United recently announced it will offer more domestic routes and budget-friendly flights. The airline will add summer flights from five of its hubs to 13 non-major cities. United will also increase flights on some existing routes and upgrade some seasonal routes into year-round options.

United will add new flights from its biggest hub, Chicago’s O’Hare International Airport, to places such as Spokane, Wash. Airline hubs help save airlines money and offer passengers better routes to their selected destinations. The four major U.S. airlines all have nearly 10 different hubs.

The added domestic routes came after United and American Airlines introduced brand new economy-class options. United and American Airlines plan to slowly roll out these new cheaper flights to most domestic destinations and eventually shorter trips to Latin America and the Caribbean

United and American Airlines made the move towards more economy-fares after Delta broke into the market last year. United plans to expand its new economy pricing beyond Minneapolis to its entire domestic roster, as the company fights to add more budget-minded consumers.

The fight to offer more economical flights comes as low-cost airlines Spirit Airlines, Inc. (SAVE - Free Report) and Frontier Airlines Inc. have gained traction. Southwest is still the most popular budget-friendly airline.