Former Conservative cabinet minister Lord Fowler has urged the party's MPs to rebel against Prime Minister David Cameron's proposals for a Royal Charter to establish a new press regulator.
He claims the Liberal Democrats and Labour's plans on a new press regulation system were imperfect but the best solution on the table.
"Leveson proposed a perfectly sensible and moderate reform: an independent board would check whether the essentially self-regulatory regime for handling complaints and ensuring fairness to the public was working properly," Fowler wrote in The Guardian.
Fowler, who is now a journalist, added: "He believed that a short piece of legislation would give the public the greatest safeguard while protecting the legitimate rights of the press.
"The Miliband-Clegg amendment is not perfect. I remain sceptical of the need for a royal charter in spite of the safeguards now written in.
"But the issue for tomorrow is quite clear: it is which of the schemes comes closest to implementing Lord Justice Leveson's careful and objective report.
"There may be a last-minute compromise, but if I was still a Conservative MP I would be voting against my party tonight."
David Cameron has insisted a cross-party agreement for a new system of press regulation protects the principle of the free press.
Labour says this is just the sort of legal under-pinning they were looking for but the Conservatives say that no such press law will exist.
Is there a chance tomorrow's Commons' votes on press regulation may not go ahead? Could there be agreement between the parties after all?