Animal charities and pet lovers fear stray cats and dogs could end up in animal testing laboratories over plans to lift a ban on their use.
The Government plans to adopt the EU-wide law allowing stray dogs and cats to be used in limited circumstances.
Liberal Democrat MP Adrian Sanders has tabled an early day motion rallying opposition to the move.
He said: "I'm shocked that the Government is considering removing the current protection given to our stray cats and dogs from being used in experiments.
"Losing a pet is distressing, but the idea that the animal could potentially end up in a laboratory is ghastly and unacceptable, and I urge the Government to reconsider."
Mr Sanders is supported by the British Union for the Abolition of Vivisection (BUAV).
It said: "If these new rules are imposed, the Government could allow the use of stray, lost or abandoned cats and dogs to be used in experiments and sentenced to a life in a UK laboratory."
A Home Office spokesman told The Sunday Times: "We can envisage no circumstances where a licence would be granted to test on strays."