British Airways pilots kicked off the first day of their two-day strike on Monday, sending over 1,500 flights into cancelation and around £80M or $98M in lost revenue. Some pilots reportedly received threats from the airlines.

According to the Telegraph, some of the British Airline Pilots' Association (BALPA) members reportedly received emails from BA, with warnings about the strike being a "serious breach" of their contracts with the airlines.

Pilots were also told that they will see one of the most popular travel perks that BA boasts of. Those who strike will no longer have the 10 percent off if they book flights for themselves while off duty.

BA has asked passengers to not appear at the airport if their flights have been canceled due to the widespread strike. The airline has already offered a number of options for passengers whose flights were canceled.

The root cause of the problem was the rejection of BALPA's proposal to implement an 11.5 percent pay increase. The pilot's organization argued that British Airways is now more financially stable than in the past and their proposal for a pay raise would not be a huge financial stressor to the company.

Aside from today and tomorrow's strikes, pilots are also scheduled to have another strike on September 27. BA said it is still willing to hold talks with BALPA "on the basis that there are no pre-conditions to those talks."

BALPA General Secretary Brian Strutton said on Sunday that pilots have been nice enough to allow for massive pay cuts when BA was facing financial crises in the past.

Strutton noted that pilots should also experience the success that British Airways is enjoying now that finances are better.

Strutton challenged BA to return to negotiations and provide pilots with "a serious offer" that should put an end to the million-dollar strikes that could take a toll not just on the airlines but also on passengers.

British Airways said BALPA did not give the airlines a detailed account of how many pilots will join the strike, CNN reported. At this point, it is unclear whether or not BA has offered anything to stop the strike.

BALPA members account for over 85 percent of the pilots who fly with British Airways. The strike was voted on by an overwhelming 93 percent of the union in July. Last week, the group said it would call off the strikes if negotiations started again.

It appears that BA has not agreed to return to the negotiating table.