(CNN) -- An American Airlines executive's threats to discipline pilots over delays and file legal action against its pilots union may poison already heated contract negotiations, a union spokesman said Thursday.
Earlier this week, American's management contacted the union to ask for talks on a new labor deal, according to the Allied Pilots Association. Then, on Wednesday, executive Denise Lynn wrote a letter to union leaders voicing concern about what she called "mounting evidence that certain pilots are engaging in an unlawful, concerted effort to damage the company."
She cited a number of issues that caused delays, including "unnecessary checks, increased and late-filed maintenance write-ups and "slow taxiing."
"I ask that you communicate immediately and unambiguously with your members that such work actions are unlawful and that any individuals engaging in such activities will be subject to both company and (union) discipline," Lynn wrote.
If the union "fails to comply with (its) legal duty" to discipline those responsible, she added, "we will have no choice but to seek appropriate injunctive relief."
Thomas Hoban, a spokesman for the Allied Pilots Association, referred to the letter on Thursday.
"This kind of threat is not conducive to good-faith bargaining and will only further serve to enrage an already frustrated and angry pilot group," Hoban said.
AMR, American's holding company, filed for bankruptcy in November. It has said the new working conditions imposed on the pilots, including greater use of flights by other airlines and more hours worked by the pilots, are necessary to be competitive with rival airlines such as Delta Air Lines, United Continental and US Airways, which have been through bankruptcy themselves in the past decade.
The airline is also proposing to freeze or terminate the pilots' pension plan and has stopped making contributions to that pension fund.
Earlier this month, American won bankruptcy court approval to throw out the pilots' labor agreement and impose new working conditions on its 8,000 active pilots. Pilots have already overwhelmingly rejected a tentative agreement that was more beneficial to its members than the rules imposed by the airline.
Since September 16, the airline has struggled. More than half its flights have been delayed, and more than 600 flights, or about 3% of its total schedule, have been canceled, according to flight tracking service FlightStats.com.
As it did in Wednesday's letter, airline management has blamed the problems on pilots for filing what it claims are frivolous maintenance reports. Management also said there has been an increase in pilots calling in sick.
The pilots union denies that there is an increase from historical norms in the number of pilots calling in sick. It also denies the maintenance reports being filed are for trivial items, saying they pose safety issues for the aircraft. But the union also says its members need to be more careful in strictly following rules given their contract situation.
American spokesmen Bruce Hicks said earlier that management has always wanted to reach a consensus deal with the pilots as it did with its other unions, and told the union it was ready to talk even before the delays and cancellations started.
"Our desire to talk has nothing to do with the operational disruptions we're seeing," he said.
CNN's Dave Alsup and Joe Sutton contributed to this report.