Spanish airline Iberia said on Friday it is suing the pilots union SEPLA and its bosses for more than EUR13 million euros (USD$17.78 million) in damages for delays and cancellations to flights since December.

It said that between December 4 and December 31 it had been forced to cancel nearly 500 flights and flight punctuality had fallen to 40 percent because of pilots operating what Iberia called an illegal work-to-rule action.

Iberia is claiming December costs including: damage to its reputation; having to contract 152 flights with other operators; and putting passengers with delayed flights up in hotels.

"The company will verify at the moment of trial what additional damage is being caused by the work-to-rule after December 31," Iberia said in a statement.

SEPLA blames Iberia's management for the delays and cancellations to flights. SEPLA said there is a shortage of pilots and poor planning.

They maintain that pilots are within their rights to work strictly in accordance with their contracts while a new collective agreement is being negotiated.

The two sides met again for talks on Friday, but no news of a breakthrough was forthcoming.