Cost-cutting plans to merge Parachute Regiment units and Royal Marines units are said to have "horrified" the defence secretary, according to newspaper claims.
The Times said one tabled cost-saving option was a combined force comprising 3 Commando Brigade, predominately made up of Royal Marines, and 16 Air Assault Brigade, which includes the 2nd and 3rd battalions of the Parachute Regiment.
The paper also reports there are plans to cut the Armed Forces' strength by more than 14,000, reducing Army numbers to the smallest since before Napoleon - fewer than 71,000.
One proposal would see a loss of 11,000 soldiers, 2,000 Royal Marines and sailors and 1,250 airmen, the newspaper reported.
Its claims have been branded "pure speculation" by the Ministry of Defence, which insists no decisions have been made.
The Times claims Defence Secretary Gavin Williamson has rejected the plans, calling them unacceptable.
An MoD spokesman said: "A whole range of options have been discussed as part of the cross-government review on how to best protect our country.
"No decisions have been taken and any talk of an outcome is pure speculation."
Defence Editor of The Times, Deborah Haynes, tweeted that Mr Williamson "was right to reject them" but that he now has to "find another fix" for the funding crisis.
The options are reportedly the outcome of a comprehensive defence and security review announced last year that has caused widespread speculation about possible cuts, amid major pressure on the defence budget.
A decision on which plan to go with was supposed to have been chosen by Mr Williamson by November 19, reports The Times.
On Thursday, Conservative former defence minister Mark Francois voiced concerns over morale across the Armed Forces, adding he was alarmed by reports which suggested that at one stage the Treasury floated a reduction in the regular Army from 82,500 to as low as 50,000.
Tory, Labour and SNP MPs have also raised concerns over the possibility of further defence cuts, while former head of Joint Forces Command, General Sir Richard Barrons, said the move would push Britain towards becoming a "Belgium with nukes".
Defence minister Tobias Ellwood said the MoD had "no intention of leaving the UK less safe".
Speaking before The Times report was published, Mr Francois told the Commons: "At a time when we face a resurgent Russia, which has carried out the annexation of the Crimea and still has further territorial ambitions in the Ukraine as well as placing pressure on the Baltic states, reducing the Army in this way would send entirely the wrong signals to the Russians about our commitments to NATO and willingness to uphold the territorial integrity of our allies.
"It would be sheer folly."
"I only have to hope that the pinstripe warriors in the Treasury, who daily live in fear that the air conditioning might malfunction or that the tea trolley might be late, have since abandoned such a daft suggestion as there's no way that I and, as (Tory MP James Gray) intimated, many of my colleagues on these benches could possibly support a reduction of that magnitude in regular manpower."
Defence Secretary Gavin Williamson is expected to reveal more about the review "shortly".
The reports of planned cuts come at a time when the Army is offering a £10,000 rejoin bonus amid struggles to meet recruitment targets.