Forty-three Israeli military intelligence reservists who signed a letter refusing to serve in the occupied Palestinian territories have been denounced as criminal by defence minister Moshe Ya'alon, as the country's political and military leadership turned its fire on the refuseniks.

The ferocity of the response was not unexpected by those involved. One signatory told the Guardian before publication that he feared being portrayed as an enemy of the state after the letter was made public.

Among those who have criticised the reservists' actions are Israel's prime minister, the president, opposition leaders and a former intelligence head. In addition, the Israeli military revealed that 200 other members of the unit had signed a counter-letter defending its work.

The reservists' letter had alleged the intelligence unit undertook "all-encompassing" surveillance of the Palestinians – whether involved in terrorism or not – and used information, including on sexual orientation, to blackmail individuals into becoming informants.

The threat of criminal sanctions would break the pattern of the treatment of reservists, including pilots, who signed previous refusenik letters who have tended to be discharged.

It is not clear, however, what charges the men and women could face. The 43 took legal advice from a prominent lawyer to ensure their letter and testimonies did not break the law, including by revealing their identities.

The text of the letter and most serious allegations were also submitted to the Israeli authorities before publication on Friday.

Since the letter was published on Friday as well asThe letter, published with testimonies from reservists of Unit 8200, claimed much of its electronic interception work was being used to support the "political persecution" of Palestinians and the continued occupation.

As a deluge of criticism of the protesters poured from senior Israeli politicians and officials, it was disclosed that the current commander of 8200 had sent a letter to members of the unit – that does interception work analogous with the US NSA or the UK's GCHQ – warning them against rising complaints with the media, saying that any ethical concerns could be dealt with adequately by commanders within the unit.

Leading the charge against the refusniks on Sunday was the Israeli prime minister, Binyamin Netanyahu. Speaking at a cyber-security conference in Tel Aviv, he accused the soldiers of "baseless slander" adding: "This is an act that should be condemned … and that constitutes political exploitation of the Israel Defence Forces [IDF].

"The IDF is the most moral army in the world and it carries out the missions that we give it to safeguard our security. From my long years of acquaintance with the members of Unit 8200, the baseless slander levelled against them will not harm the vitally important work they do for the nation's security. And I say to them – continue."

Netanyahu's comments came as an IDF spokesman, Brigadier General Motti Almoz, wrote on his Facebook page on Sunday that the refuseniks would face "the disciplinary treatment [that] would be sharp and clear". He added: "There is no place for refusal in the IDF. There are arguments and there are political stances. Celebration of democracy. ... What happened here, in my eyes? Exploitation of military service to express a political stance."

The most furious condemnation came from Ya'alon, who described the letter as a "foolish and obscene attempt to support the international false delegitimisation campaign against the State of Israel and the soldiers of the IDF".

By Monday Ya'alon, speaking at the same cyber-security conference as Netanyahu, was also hinting that the reserve soldiers could face criminal prosecution. "Their refusal is politically, not morally, motivated. Soldiers should go to their commanders when they have a problem. Our officers and soldiers are doing sacred work which saves many lives and they deserve our gratitude. I will not allow a political abuse of this and those who signed this [refusal document] will be treated as criminals," he said.

Other political figures who have joined criticism of the letter include several prominent members of Israel's opposition.