A union representing 11,000 American Airlines fleet service workers on Thursday suspended a tentative contract deal struck last week.
The Transport Workers Union said in a statement that "certain issues on the bargaining table had not been resolved."
The deal covered a portion of TWU's members at American -- workers who handle baggage, clean aircraft, and fuel planes. TWU represents 25,000 workers at American in seven different groups.
Union negotiators tentatively agreed to the airline's offer last week but had planned on recommending that members vote no.
"If we can't recommend it, we're not sending it," TWU International President James Little said in the statement.
American Airlines believes the deal was fair and can still be worked out, company spokeswoman Missy Latham said in a statement.
"We will work with the TWU to understand their concerns," she said. "We expect that we can resolve any issues."
The airline remains in negotiations with other labor groups, most notably pilots and flight attendants.
Talks with the Association of Professional Flight Attendants broke off in Washington on May 21 after members authorized a strike. Federal mediators have not announced their next step.