US Airways has raised its hostile offer to buy Delta Air Lines for $10.2bn (£5.2bn), after Delta rejected a previous $8bn bid in December.
Delta has said it will look into the revised unsolicited offer
The offer is 20% higher than last month's offer and aims to create a merger of the two firms.
The management of Delta, however, wants the firm to emerge from bankruptcy protection as a stand-alone entity.
Delta has said it will fulfil its duty to review the revised "unsolicited merger proposal".
According to a statement by US Airways, the new offer values Delta at between $12.7bn and $15.4bn, in comparison with $9.4bn and $15.4bn as defined under Delta management's proposal.
"It is time for this process to move forward," said US Airways chairman and chief executive Doug Parker.
He added: "We continue to believe that this is the right time to create a better airline that provides more choice to consumers, increased job security for both airlines' employees."
Delta, however, argues that the new proposal fails to take into account "significant concerns that have been raised about the initial US Airways proposal and would increase the debt burden of the combined company by yet another $1bn."
The new offer, which expires on 1 February, would give Delta creditors $5bn in cash - up from $4bn - and 89.5 million US Airways shares, up from 78.5 million shares.
Delta hopes to emerge from bankruptcy in the next six months as an independent airline.