Imam Khomeini (ra) and other grand maraji’ have stated:

It is obligatory upon each and every Muslim to refrain from buying or using products, that the production and purchasing of bring profit for the Zionist regime, which is currently at war with Islām and Muslims. It is also obligatory to abstain from importing or promoting products which the manufacturing and selling of benefit Zionism.

As a whole, any sort of transaction that is to the benefit of the occupying Zionist regime, which happens to be the enemy of Islām and the Muslims, must be completely avoided. To import or promote their products, which would profit or benefit them is also impermissible, since purchasing such products brings harm and difficulties for Muslims (by strengthening Israel).[1]

Answers from other maraji’ taqlīd:

The Office of His eminence, Āyatullāh al-‘udhma Khāmene’I (may Allah prolong his life):

Generally speaking, the buying and selling of any product imported from the occupying Zionist regime is forbidden. The same applies to buying and selling any type of product from Zionist companies, or companies which help and profit Zionism. It is the duty of the duty bound (mukallaf) to identify in which cases the rule is applicable. In the event where it is not established that a product’s income is profitable for Zionism or is used against Islām, there is no problem in using it.

The Office of His eminence, Āyatullāhal-‘udhma Sistani (may Allah prolong his life):

If it is established that some companies give [even] a portion of their profits to help strengthen the Zionists, it is impermissible to enter into transactions with them.

The Office of His eminence, Āyatullāhal-‘udhma Makarim Shirazi (may Allah prolong his life):

No, it is not permissible to do so (buy or sell such products), except when necessary, and only to the extent necessary.

The Office of His eminence, Āyatullāhal-‘udhma Saafi Gulpaygani (may Allah prolong his life):

It is evident for every Muslim who is aware of the political situation of the world the vile goals of the enemies of Islām who are working within Muslim countries, and all other countries to achieve their lowly objectives.Their aim of damaging the economies, plundering the wealth of nations and more importantly pillaging the spiritual wealth of the Muslims whilst propagating and promoting a culture of Kufr and non-Islāmic ideals. Any sort of transaction or relation that would help strengthen them is forbidden, and it is upon the Muslims to strive for severing all ties with them from the Islāmic countries, and to prevent them from gaining political and economical hegemony.

His eminence, Āyatullāh Hadavi Tehrani’s view on the matter:

With attention to the danger posed by Zionism to the Islāmic world, in fact to humanity, any action that results in the strengthening of this despicable movement is absolutely forbidden. With this in mind, buying and selling products that in any way help strengthen Zionism is impermissible, except in cases where it is necessary, only to the extent necessary. It is upon the duty bound (mukallaf)  to specify such cases. Although, if it is not proven [that they support Israel], there is no objection [in buying or selling such products].