Members of the two bargaining units voted "no" on the contract offer, which was reached with American in May. Mechanics voted against the agreement with 64 percent opposed, while 54 percent of stock clerks voted against it.
But technical specialists, a third bargaining unit, ratified the deal with a 77 percent vote. The airline said approximately 90 employees are represented under the maintenance control technician contract.
"These employees will realize immediate financial gains, along with more vacation days, holidays and sick time," American Airlines spokeswoman Missy Lathan said in a statement.
Maintenance control technicians provide technical oversight for troubleshooting aircraft maintenance issues in the field, oversee the approval process for the minimum equipment list and serve as the maintenance point of contact for flight crews and line maintenance mechanics.
The two "no" votes rejected the contract offers -- and authorized a strike if necessary.
In order to strike, the National Mediation Board would have to release the Transport Workers Union from negotiations. The union would also have to wait out a 30-day "cooling-off" period.
In a statement, TWU International Vice President Garry Drummond, who heads the union's Air Transport Division, said its members had "spoken loud and clear."
"After four years of negotiations, a majority of TWU members in our mechanic and related and stock clerk groups were not convinced that this agreement represented an adequate return for the hundreds of millions of dollars of sacrifices we agreed to in 2003 to keep American planes in the air and prevent our employer from filing for bankruptcy. However, for workers in our technical specialist group, salary increases and improvement in benefits were enough for passage."
Latham said the airline expects to continue working toward new agreements with the two groups that did not ratify the contracts.
"American felt the tentative agreements reached with both groups represented the company's best offer and demonstrate we can reach agreements with the TWU," she said.
American is also in long-running contract talks with its pilots and flight attendants.