Squealer's justification came after Napoleon made the announcment of the possibility of the hens providing eggs for trade.
To convince the animals, Squealer said,
Are you certain that this is not something you have dreamed, comrades? Have you any record of such resolution? Is it written down anywhere?
No such record existed, so the animals were convinced that Squealer was right and that they would have to accept that the hens would give up some eggs.
In the book "Animal Farm" the animals have begun to change from animals desiring independence from human ways to political imitations of the humans. The pigs start breaking the commandments that had been established and they develop excuses and use fear tactics to control the other farm animals.
One of the commandments was that they would not enter into any trade agreement or exchange goods with humans. However, the animals become aware that this is going to happen. At first they find out through rumors.
As winter came the animals ran out of grain and were starving. Napoleon called a meeting with his dogs at his side. Squeller ordered that the hens would have to lay eggs and they would be traded with humans for food. The hens were angry and called it murder. They flew overhead dropping their eggs on the ground.
Napoleon responded by telling them they would receive no more rations and anyone giving them any would be put to death. The dogs enforced the proclamation.