The Northern Ireland Council for Voluntary Action (NICVA) has called on Secretary of State Karen Bradley to restore decision-making at Stormont.
The voluntary and community sector umbrella body said Brexit, education, health and public finances are at risk.
There has been no executive since January 2017, when the DUP and Sinn Féin split in a bitter row.
"Future generations will not thank us for ducking these issues," said NICVA chief executive Seamus McAleavey.
"The challenges we are facing as a society cannot be dealt with by a hands-off, 'do nothing' approach that relies on short-term fixes to long-term issues," he said.
Northern Ireland's power-sharing Assembly collapsed over the Renewable Heat Incentive (RHI) scheme.
That led to a snap assembly election in March last year, which saw the DUP and Sinn Féin re-emerge as the largest parties, but so far they have been unable to reach a deal to restore the institutions.
NICVA is currently surveying its 1,100-member organisations to find out how the absence of a functioning government is affecting them and the people they work with, and asking their views on the future.
"It is NICVA's belief that only a functioning government with decision-making ministers can bring an end to the deadlock," added Mr McAleavey.
"While it continues, we are storing up hundreds of unmade decisions and ever greater problems that will be harder to deal with the longer they go un-tackled.
"The secretary of state needs to act today, to restore decision making in Northern Ireland."
SDLP leader Colum Eastwood said legislators should be embarrassed by the length of time Stormont has been out of action and that with Brexit looming the impasse must not go unchallenged.
"With Brexit our politics has now reached a defining moment. We cannot allow a hard Brexit to be thrust upon our people without a functioning Assembly to mitigate its devastating impacts."
Ms Bradley was appointed secretary of state in January after the resignation of James Brokenshire due to health reasons.