Private equity group Terra Firma officially launched its agreed 2.4 billion pound ($4.7 billion) bid for music group EMI on Wednesday, effectively setting a June 27 deadline for any counter-bids.
EMI said last week it had agreed to the 265 pence a share cash bid from Terra Firma, but sources familiar with the situation have told Reuters that long-term suitor Warner Music Group is still examining the financial data.
Former EMI Music Chief Executive Jim Fifield has also said he wants to buy his former company.
In a statement to the stock exchange, Terra Firma said the offer document was being posted on Wednesday, and acceptances of the offer should be received no later than 13:00 British Summer time on June 27.
Terra Firma has offered 265 pence a share, but EMI's stock has since traded above 270 pence, implying the market expects a higher offer.
Analysts have speculated that Warner would have to offer above 280 pence to compensate for the fact that any trade deal would be subject to scrutiny by European regulators.
A separate deal that created the Sony /BMG group is still being investigated in Brussels, and it is not clear whether any Warner-EMI tie up would be approved.
Alternatively, Warner could consider waiting until the regulatory outlook is clearer and offering to buy the EMI Music division, which represents such artists as Norah Jones and Coldplay, from Terra Firma.
Warner has not commented publicly on its intentions.