BERLIN (AP) — Lufthansa's operations were disrupted Sunday at Frankfurt airport because of technical problems, German news agency dpa reported.

Check-in systems on the airline's website and at the counter, as well as boarding, were affected at Germany's biggest airport, a Lufthansa spokeswoman told dpa. Some flights were delayed or would have to be canceled because of the problems.

Check-in was still possible using cellphone browsers on smartphones or tablets, and the Lufthansa app.

The technical problems were caused by external IT service providers, dpa reported. Lufthansa asked travelers to check the status of their flights and said it was working with “high-pressure" to resolve the issues.

Last month, cable damage during construction work in Frankfurt caused Lufthansa computer systems to fail, resulting in flight cancellations and delays worldwide.

Sunday's problems came a day before a national strike in Germany is set to bring the country's traffic to a standstill with airport, train and public transportation employees all protesting for higher salaries in a one-day walkout on Monday.

Air traffic was already canceled on Sunday at Germany's second-biggest airport in Munich because of the upcoming strike.