Ministry of Natural Resources investigators have joined the probe at the Toronto Humane Society.
The facility was raided last Thursday by animal welfare officials armed with a warrant and animal cruelty charges were laid against five employees.
OSPCA lead investigator Kevin Strooband says the provincial ministry officials are working under their own warrant - which expires at 6 p.m. today - investigating allegations that laws governing the release of raccoons into the wild were broken.
Strooband says the legislation calls for raccoons to be released within a one-kilometre radius to prevent the spread of rabies and other disease and it's alleged the humane society released raccoons further afield.
He adds the OSPCA's task of checking animals at the shelter is only about 25 per cent complete and the investigation could last a few more weeks.
The OSPCA has said animals were found in appalling conditions and seven had to be put down.
The society has said it would challenge the OSPCA search warrant, claiming its scope is too broad.