Panama City (AFP) - Dozens of pilots with Panama's main carrier Copa Airlines protested outside Panama City's international airport on Thursday in an intensifying campaign for higher pay.

Their union, UNPAC, is warning of an indefinite strike by Copa pilots starting next week, from June 15, unless the demands are met.

Panama is a major Latin American hub, and a stoppage could throw travel plans for thousands of passengers into disarray.

Some American and European airlines rely on Copa code-shares to carry their passengers to and from destinations in North, Central and South America.

UNPAC represents 1,600 pilots, two-thirds of whom work for Copa.

It is demanding a 36 percent pay rise, but the airline is offering only around 10 percent, UNPAC secretary general Luis Young told AFP.

The pilots are also demanding they be paid more according to seniority, and for time spent planning flights.

Copa employs around 9,000 people, including pilots, flight attendants and ground staff.

In a statement, it expressed confidence a "fair accord" would be reached.

"We do not expect any interruption to services or operations," it said.