United Airlines Holdings Inc. is offering its pilots a contract with an incremental value in excess of $8 billion over four years, making it the richest labor deal for a mainline U.S. carrier, Bloomberg News reported Tuesday, citing the company's chief executive.

The move comes at a time when pilots in North America are pushing for better pay and working conditions during their talks with company managements over new employment contracts.

Delta Air Lines' landmark pilots contract, which offers $7 billion in higher pay and benefits in March has put pressure on rival carriers to hand out similar deals ahead of a busy summer travel season.

United's CEO Scott Kirby told Bloomberg News that the company has been negotiating weekly to reach a formal agreement with the union.

However, he didn't give details on the value of the pay, benefits and quality-of-life improvements included in the proposal other than to say that it would top the recent deals agreed to by its two biggest rivals, as per the report.

United did not immediately respond to a Reuters request for comment.