A regional officer for the union, Alan Scott, who has been working with the charity on its redundancy consultation, told Third Sector that Shelter had originally said the number was 80, but fell to 44 after a consultation.
Scott said the charity, which has 933 employees according to figures on the Charity Commission website, had reduced the number by using some of its voluntary income to bolster services for which funding had been cut.
He said the redundancies were necessary mainly because of contracts coming to an end or being transferred to other organisations. Cuts in legal aid were another factor, he said.
"Ideally, there would be no redundancies in an organisation that has voluntary income," said Scott. "But it's reasonable that if someone else is going to be providing a service instead, there's no point in trying to compete with them."
A spokeswoman for Shelter declined to comment on the figures, but said it had been consulting on the closure or reduction of a number of services around the country after losing some contracts.
"Unfortunately, this has resulted in the need for a number of redundancies," she said. "Shelter is managing these as sympathetically as it can, while ensuring it continues to meet the ever-increasing demand for its services at this incredibly challenging time."