Critics say the government does not understand the threat posed to the TA
A Labour MP has called on Gordon Brown to intervene to reverse the controversial planned reduction in training for Territorial Army units.
Lindsay Hoyle said ministers would have to give more ground due to the scale of opposition and compared the issue with that of Gurkhas' residency rights.
In future, TA units which are not due to be deployed to Afghanistan will be limited to training one night a month.
Ministers said this would be kept under review but ruled out more concessions.
On Monday they backtracked on plans to suspend all routine TA training for six months, offering a compromise of one night a month.
At the moment, most units train one night a week as well as one weekend a month.
Nearly a dozen Labour MPs have now publicly criticised the scaling back, a move approved by military chiefs earlier this year to ensure resources were prioritised for the regular army.
Among those expressing concern about the possible impact on recruitment and retention of territorials include former defence secretary John Reid and ex-defence aide Eric Joyce.
Mr Hoyle said the original decision had been "crass" and the fallback position of one night's training a month was "not good enough".
"This is an absolutely ludicrous position that the government has got itself into," he told the BBC's World at One programme.
He said territorial training was not like a "tap you can turn on and off" and he urged the prime minister to find the money to "ensure that the TA is back in its rightful place".
"We actually need the prime minister to personally intervene and say: 'Look Land Command, you have got this wrong. I want to make sure the money's there, let's find the money from somewhere'," he said.
He likened the situation to that of the Gurkhas, on which the government had to do a U-turn after it lost a Commons vote on their settlement rights in April.
The Conservatives have forced a parliamentary debate on the issue of territorial training on Wednesday.
However, Mr Hoyle said he would not be voting with the opposition in the debate, accusing the Tories of "naked opportunism" over the issue.
The TA is made up of volunteers who commit their spare time to training as soldiers and working with the regular army.
It is divided into independent units who recruit locally and national units who recruit across the UK.
All TA soldiers who are mobilised have their civilian jobs legally protected
Conservative MP Mark Lancaster, a current reservist, said the cutback in training was "terribly short-sighted" and would particularly hurt those with specialist skills such as bomb disposal.
He said he was "sure" the government could find the money from somewhere to plug the remaining £17.5m hole in the TA's 2010 budget.
Armed Forces Minister Bill Rammell said it was "critically important" people understood that pre-deployment training for those due for active service in the near future would not be affected by the changes.
"We would not send people into battle unless they had the appropriate training and support," he said.
Ministers had "listened and responded" to criticism of the original plans, he said, and stressed the situation would be kept under "constant review".
But he rejected claims the plans threatened the TA's very existence.
The future of the TA has risen up the political agenda in recent weeks with more than 500 reservists now serving in Afghanistan.
With the Army focusing its resources on the Afghan mission and boosting recruitment of full-time soldiers, ministers say "tough decisions" are needed over budgets in other areas.