Labor unions at US Airways will meet with CEO Doug Parker and senior management April 29 to discuss concerns and "critical issues" that they say remain unresolved since the merger of US Airways and American Airlines in December.

When Parker and his team pulled off the $11 billion deal, endorsed by pilots and flight attendants at American, the combination to create the world's largest airline appeared to have the blessing of labor at both companies.

But four months later, five US Airways unions say they aren't happy with the way things are going.

Leaders for the flight attendants, pilots, machinists, fleet service, mechanical, dispatchers and simulator engineers wrote to Parker this month that they were "proud to have supported a merger" but "expect management to move forward immediately to keep its commitments to all of its employees and make this the best airline in the world."

The issues include job security, seniority, compensation, scope, benefits, and working conditions, the letter said.

American Airlines spokesman Todd Lehmacher said, "We want to work together to reach joint collective bargaining agreements with all our unions - agreements that will benefit the employees of American and US Airways equally."

The April 29 meeting is a regularly scheduled quarterly meeting that Parker hosts with union presidents from American and US Airways. The meetings follow each quarterly earnings report.

In July 2012, unions for more than 30,000 US Airways employees formed a coalition to coordinate issues related to a potential merger. At the time, six unions were in contract negotiations or mediation - some for as many as seven years, the letter said. "Many US Airways employees had suffered from airline consolidation that too often had been advanced at the expense of airline workers."

The letter outlined specific problems:

Contract talks with Transport Workers Union Local 544, representing instructors and simulator engineers, have been "put on the back burner."

US Airways dispatchers, in TWU Local 545, earn 25 percent less and work six weeks more than American dispatchers.

Mechanics and fleet service workers, represented by the International Association of Machinists (IAM), "were in negotiations premerger, then ignored by labor relations while it negotiated with stand-alone American employees." The IAM has asked the National Mediation Board to be released from contract talks, triggering a 30-day cooling-off period, and potential strike.

Customer service agents, jointly represented by the Communications Workers of America and the Teamsters, said, "The vendors working for American are encroaching on our work at some locations and forcing the association to file grievances."

US Airways pilots said the airline's labor relations personnel have "failed to implement the required work rules and contractual provisions to bring equality to the pilots of US Airways," the letter said.

"Everybody seems to think everything is rosy, and that's not true," said Capt. James Ray, spokesman for the US Airways pilots union, referencing the labor problems. "The pilots have a contract, but the company is dragging its feet on implementing some sections of the contract.

"Several other employee groups don't have a contract and are very frustrated," Ray said. "The IAM [mechanics] are prepared to strike if they cannot settle their contract soon."

Separately, the US Airways pilots union in March filed a lawsuit asking for a federal arbitrator to decide how the seniority lists of American and US Airways pilots will be integrated. Seniority is key to routes, pay, schedules, and aircraft flown.

The US Airways pilots union wants the parties to use a process in a federal law, known as McCaskill-Bond, to decide how to integrate pilot seniority. McCaskill-Bond was passed by Congress in 2007, after American purchased Trans World Airlines. TWA pilots were placed toward the bottom of the seniority list and were later furloughed during an economic downturn.

US Airways pilots want a voice in how seniority is decided. Their concern is that American's Allied Pilots Association could be named the bargaining agent for all pilots at both airlines before a seniority agreement is reached.