Lord Goldsmith has been sacked as an environment minister, amid fears that animal rights could be downgraded under Liz Truss's Government.
The peer has been removed from his post covering domestic animal welfare, but will retain another position at the Foreign Office, where he is minister of state for the Pacific and international environment.
It comes two months after Lord Goldsmith, who backed Ms Truss for the Conservative leadership, used Twitter to attack Mark Spencer, who has been appointed minister of state in the environment department.
He wrote: "Mark was the biggest blocker of measures to protect nature, biodiversity, animal welfare."
The sacking comes after Downing Street said the reshuffle had been halted during the period of mourning following the Queen's death.
The Telegraph says he issued what appeared to be a warning to Ms Truss, saying: "We have so much more to do to turn the tide here.
"The UK is, after all, one of the world's most nature-depleted countries. But, if Defra continues to get the backing you need and deserve across government, you can and you will turn the tide."
Fantastic champion
One Tory MP, Henry Smith, said: "Zac has been a fantastic champion of animal-welfare issues in government and, despite all the other distractions, he's been instrumental in delivering quite a few pieces of legislation that have made it on to the statute books.
"I would expect the government to fulfil all its manifesto commitments and pledges on animal welfare, regardless of which individuals occupy roles in various departments."
Animal-welfare campaigners are concerned that under Ranil Jayawardena, the new environment secretary and a former trade minister, farmers could be undercut on animal welfare grounds in trade deals.
Some Tory MPs believe Ms Truss may be planning to drop the kept-animals bill, despite Mr Jayawardena telling the Commons last week that its passage would resume as soon as possible.
One MP said: "Liz might abandon it. She had no interest in animal welfare while a minister in Defra."
There are also fears that the trophy-hunting ban, which Lord Goldsmith had championed against opposition from some Conservative backbenchers, could be dropped. That would mean that importing parts of endangered animals shot abroad would be allowed to continue.