By Rajesh Kumar Singh

CHICAGO American Airlines and its pilot union have begun negotiations to improve the tentative contact agreement after the company's CEO spoke with the union's chief on Tuesday, according to a union memo seen by Reuters.

The Texas-based carrier's pilots are due to start voting Monday on a new four-year deal that provides for a pay increase of about 42% and other benefits. But the Allied Pilots Association (APA), which represents American pilots, warned that the ratification of the deal was in "jeopardy" after United Airlines raised the benchmark with its own deal.

"Our respective bargaining teams have committed to working around the clock beginning tonight for the next few days to address crucial improvements to the TA (tentative agreement)," APA's head Ed Sicher told the pilots in a memo on Tuesday.

A union spokesperson said the talks began on Tuesday and will continue on Wednesday.

American Airlines declined to comment.

(Reporting by Rajesh Kumar Singh, Editing by Franklin Paul)