Hartlepool MP Jonathan Brash, alongside Andy McDonald, Anna Turley, Chris McDonald, Lola McEvoy and Luke Myer, said the situation was an “immediate crisis”.
The joint letter states: “While we acknowledge that Defra has noted multiple possible causes for seal mortality, including disease, the unprecedented scale of losses in the Tees estuary requires urgent and coordinated action.
“In similar situations internationally, governments and wildlife authorities have taken proactive steps to investigate causes, mitigate risks, and protect marine mammal populations.”