Margaret Curran, Labour's health spokeswoman, said: "I want to know why in the chamber last week Alex Salmond said Nicola Sturgeon had been informed throughout, I want to know why Nicola Sturgeon said she knew on Tuesday, when it actually appears that she knew well before that.
"It goes to the heart of the measures that are in place to make sure that we control such serious outbreaks."
She added: "There are also serious questions to be asked as to why her [Sturgeon] department, and she has control of that department, did not know earlier and why they did not take the necessary steps."
However, the government said the claims over unnecessary deaths were "completely without foundation".
Public Health Minister Shona Robison echoed that stance and described the allegations as "unfortunate".
Speaking to BBC Radio's Good Morning Scotland programme, she said: "I think it's better to wait until the cabinet secretary [Sturgeon] makes her statement."
At the weekend Ms Sturgeon said there was a "compelling case" for an independent inquiry at the hospital.
She also said serious questions had to be asked of the authority running the Vale of Leven Hospital in Alexandria.
NHS Greater Glasgow and Clyde launched an inquiry in May due to fears the infection had been passed between the Vale of Leven Hospital and the Royal Alexandra Hospital in Paisley.
It found higher than expected levels of C.diff in January, February and May.
Ahead of the statement to parliament, Scottish Conservative MSP Mary Scanlon said she was keen to see the setting up of an independent inquiry.
She said it was important to learn from the experience at the Vale of Leven and to ensure that in future "all NHS health boards follow the protocols and procedures in response to infections in hospitals".
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.
Bookmark with:
What are these?