Labor disputes increased in two U.S. airlines Thursday, with one confrontation escalating amid threats of legal action.

The Wall Street Journal reported that flight attendants for US Airways rejected a contract proposal that would have put them under the same terms as their counterparts at the former America West Airlines for the first time since both airlines merged seven years ago.

In a statement, officials at the Association of Flight Attendants-CWA said US Airways did not do enough.

"For too long, the flight attendants have subsidized the cost of the merger," the statement said. "Management has failed to adequately address these concerns."

US Airways had been seeking to remedy their attendants' concerns while also pursuing a merger with AMR Corp., the parent company of American Airlines, which, according to NBC News, has been embroiled in its own labor dispute since last week.

American has blamed pilots for a drastic increase in flight delays and cancellations. Of the company's 7,500 scheduled flights this week, only 57 percent have arrived on time, compared to an 82 percent punctuality rate this time last year. Last week, the company also cancelled more than 300 flights, blaming an increase in maintenance requests by crews and what it called "sick-ins," coordinated sick leave requests by pilots.

The Allied Pilots Association (APA) has denied the accusation.

"We do not want to pursue a legal remedy," an airline spokesperson told NBC. "But we will be left with little alternative if APA does not take action to stop those pilots who are intentionally harming the operation."

According to The Dallas Morning News, the company's senior vice president of people, Denise Lynn, sent the APA a letter making a similar threat if it did not stop members from what it called "unlawful conduct."

"The conduct at issue is inflicting economic damage on the Company," Lynn said in her letter. "It is frustrating and alienating our customers; and it is driving unnecessary work and significant stress for other employees. If this conduct continues, it will diminish the value of the Company and the ultimate return to our creditors."

National Public Radio reported that the letter came a day after the APA announced negotiations with the airline would be continuing through Friday.

"Within 24 hours of being invited back to the bargaining table by this management team, they fired off a letter that essentially threatens legal action against the pilots," APA officer Tom Hoban told NPR. "In that regard, it's like a baseball bat with an olive branch wrapped around it, and they just hit us up the side of the head here. It just doesn't make any sense."

NBC News' report on the dispute at American Airlines, aired Thursday on NewsNation with Tamron Hall, can be seen below.

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