"Planning and organisation for 2014's SAWS workers needs to be under way now," the letter stated.
"We are currently in a hiatus position, not knowing how many licensed workers the industry will be able to recruit, and from where, without clarity from government about the future of the scheme."
In the letter, the representatives called for a "scalable" replacement and then concluded: "An early decision is vital."
A Home Office representative said: "A response to the Migration Advisory Committee report will be made in due course."
But he added: "We can't currently give a time-frame."