The US Federal Aviation Administration has intensified its investigation into airlines it claims did not comply with flight reductions during the government shutdown.
The agency ordered carriers at 40 major airports to cut daily flights in early November. The measures were designed to ease pressure on air traffic controllers working without pay.
The FAA has sent letters to airlines that operated more than ten daily flights at these airports.
If found not to have complied, companies faced fines of up to €69,000 per flight for exceeding limits.
