A stunning oversight that allowed a man convicted of attempted murder to be invited to a party in India with Prime Minister Justin Trudeau is prompting many to say the Canadian government is too close to Sikh separatists.

Former Cabinet minister Ujjal Dosanjh has long accused his old party of being too close to Sikh separatists but says inviting Jaspal Atwal to a reception was the last straw.

Atwal was convicted of attempting to kill an Indian Cabinet minister in 1986. He was also charged, but not convicted, in connection with a 1985 attack on Dosanjh, a staunch opponent of the Sikh separatist movement's push for an independent state of Khalistan.

Trudeau's office says the invitation was a mistake. However, Atwal was photographed with Trudeau's wife earlier in the week.