The buyout proposal is valued at $24 a share, including $20 to $22 a share in cash.
The company said it had received a $28.75-a-share buyout proposal from an investor group led by its chairman.
Lord King said he might consider organizing his own buyout proposal, but was not likely to do so soon.
The board had given the unions until today to present a buyout proposal.
The company's stock was trading around $56 a share before he made his $75-a-share buyout proposal.
The company said it would name a special committee to review the buyout proposal if one is made.
Ticketmaster, which is growing more slowly, was less opposed to the buyout proposal.
But the particular buyout proposal being pushed through the House is especially harmful.
The board, in its statement Monday, also left the door open to a buyout proposal from employees.
The letter was part of his campaign by to renew the urgency in getting a new buyout proposal together.