Cabin crew at South African Airways (SAA) went on strike on Wednesday over pay benefits, the top union at the state-owned carrier said, disrupting domestic flights and threatening to extend the walkout to international routes.

The South African Cabin Crew Association (SACCA) said its nearly 1,400 in-flight workers would down tools indefinitely.

SAA said the strike had already delayed flights out of O.R. Tambo Airport in Johannesburg, which handles around 19 million passengers a year, and would also affect flights from its coastal airports.

Zazi Nsibanyoni-Anyiam, president of the SACCA union, told Reuters that the workers, who represent around 80 percent of SAA’s cabin crew, had not received pay increases for six years.

“We will be here until the company puts an offer on the table. We think what we are asking for is reasonable,” Nsibanyoni-Anyiam said from a picket outside O.R. Tambo Airport.

SAA, which is technically insolvent and reliant on government debt guarantees of almost 20 billion rand ($1.52 billion), has been singled out by rating agencies as a threat to the country’s credit status, which was recently downgraded to “junk” by two of the big-three ratings agencies.

($1 = 13.1375 rand)

(Reporting by Mfuneko Toyana; editing by Jason Neely)