Two major budget airlines canceled hundreds of flights over the weekend amid bad weather conditions and air traffic control issues, with JetBlue Airways leading the way in canceling 13% of its scheduled Sunday flights. The American low-cost airline just last week placed a bid to buy Spirit Airlines even as the latter is already considering a merger with Frontier.

Data from FlightAware, which tracks real-time flight information, revealed that JetBlue canceled 148 flights Sunday, while Florida-based Spirit Airlines canceled 140 flights on the same day. JetBlue canceled more than 330 flights over the weekend, while Spirit canceled more than 470 flights, The Hill reported. Also on Sunday, JetBlue reportedly delayed 84 flights to and from Boston, with the said flights accounting for 30% of Sunday’s schedule, WCVB-TV reported. A day earlier, the airline pushed back 117 flights.

In a statement to Boston.com, JetBlue said severe weather and issues with air traffic control on the East Coast affected weekend schedules. A JetBlue spokesperson said that “despite hiring more than 3,000 new crewmembers already this year, like many businesses, we remain staffing constrained and these disruptions exacerbate an already challenging staffing situation,” NBC Boston reported. The company said it is “working to cancel flights in advance whenever possible” to give passengers time to “adjust their plans and do not need to show up to the airport.”

In a memo to employees, COO Joanna Geraghty said that poor weather conditions and delays related to ATC contributed to “cascading problems” in April, USA Today reported. Geraghty assured JetBlue workers that “our #1 priority right now is the operation.”

JetBlue’s canceled flights came about a week after the airline put up a bid to purchase Spirit Airlines for $3.6 billion. Spirit is up for a $2.9 billion merger with Frontier Airlines, but Spirit’s board of directors announced that they will evaluate the JetBlue offer.

After the Spirit bid was announced, JetBlue CEO Robin Hayes and Geraghty wrote a letter to the employees, saying that while “Spirit has a very different brand and product” from the Queens-headquartered airline, the two airlines “would be a perfect match” after certain considerations, CNBC reported.

Some analysts pointed out that a JetBlue-Spirit merger may result in higher fares for consumers. Investment banking firm Raymond James downgraded its JetBlue stock rating to neutral following the announcement. Analyst Savanthi Syth said the move was an “indecent proposal.”