The Green Party is linking the retirement of Health Minister Tony Ryall to accusations it has made that he failed to act on allegations involving the misuse of public money.
Mr Ryall plans to leave Parliament at the election later this year, but will retain control of the health and state-owned enterprises portfolios until then.
Last week he denied allegations by the Greens that he has known for years about claims a GP group was using Southern District Health Board money without authorisation, and that he did nothing.
Greens health spokesperson Kevin Hague says he believes there is a link between that matter and Mr Ryall's resignation. "His answers in the House last were both evasive and contradictory, and also implausible. His account of the whole affair is very hard to believe."
Mr Ryall says there is no link.
Mr Hague said last week that the minister has known about a suggestion of fraud since 2010 but Mr Ryall said there is no record of that and he has no recollection of getting such advice.