The UK has set a date by which Spain's Grupo Ferrovial must either make a firm bid for British airports operator BAA or leave the firm alone.
Ferrovial is eyeing the UK market
The takeover panel announced the "put up or shut up" deadline was set for 24 April at noon.
BAA recently rejected a £8.8bn (12.7bn euros; $15.3bn) takeover bid from a consortium headed by Ferrovial.
BAA, which runs seven UK airports including Heathrow and Gatwick, said the offer undervalued its assets.
Ferrovial said it was satisfied with the deadline. "We are very comfortable working within the regulatory environment and within the timeframe," a spokeswoman for the company said.
She said: "We are still talking to BAA shareholders and still have the option of walking away."
Australia's Macquarie Bank has also been considering making a rival bid.
Following the news, shares in BAA fell 0.24% to 837.5 pence in mid-afternoon trading.