The Standards in Public Office Commission has been prevented from advancing any current or new investigations into alleged political wrongdoing, RTÉ's This Week has learned.
It is understood that the board of the political standards watchdog has received legal advice.
The body said it requires its full complement of six board members to investigate allegations against politicians or political parties.
Two posts at the Commission fell vacant last week, including the post of chairman held by former High Court judge Matthew Smith.
Appointments to the board must be made by the Oireachtas on the recommendation of the Minister for Public Expenditure and Reform, Brendan Howlin.
A spokesperson for the minister told RTÉ's This Week that Mr Howlin was aware of the vacancies at the board and he would take steps to have the posts filled by the end of next month.
As a result, a number of high profile investigations either under way or under consideration by SIPO cannot be advanced.
However, speaking to RTE's This Week programme, former Fine Gael minister Lucinda Creighton said steps should have been taken to have filled the vacancies in advance.
She said it was an "urgent" matter to be resolved given the fact that January is one of the busiest months of the Commission's workload.
The investigation shut down comes as the standards body is engaged in a separate stand-off with the Minister for the Environment Phil Hogan.
Last week he blocked the Commission from introducing new reforms aimed at making smaller units of all political parties accountable under new accounting guidelines.
As RTÉ's This Week revealed, Mr Hogan has accused SIPO of acting outside its legal remit but the Commission said it is certain it has acted correctly.
Sinn Féin Public Expenditure and Reform spokesperson Mary Lou McDonald has said the Government should have prioritised the appointment of SIPO board members before the Christmas break.
Ms McDonald said: "Given the important work that SIPO is engaged in this situation should have been given the appropriate priority ahead of the Christmas break. Instead it [the Government] has dropped the ball and put important investigations at risk."
Regarding the stand-off between Mr Hogan and SIPO Ms McDonald said it is "unacceptable" that the minister would engage with the commission in "such a heavy handed manner."
If he feels that the commission has acted outside of its remit then he should sit down with them and engage in face-to-face dialogue, she said.