JetBlue Airways said Tuesday it made an unsolicited $3.6 billion bid for Spirit Airlines, potentially snarling merger plans between the ultra-low-cost carrier and Frontier Group Holdings.

JetBlue offered $33 a share all cash, about 33% higher than Frontier’s offer of 1.9126 shares of stock and $2.13 in cash, which would value Spirit at $24.93 per share as of Tuesday’s closing price.

Shares of Spirit closed up 22% at $26.92, their highest level since mid-February. Sprit’s 52-week high is $39.19. Just before COVID-19 lockdowns became widespread, Spirit shares traded around $45.

Read more: Reuters