Let us see some of the accusations of vedantins
Bhaskara (9th Century CE), the propounder of bhedabheda-siddhanta was one of the earliest Indian philosophers to attack Mayavada. In his commentary on Vedanta-sutra, Bhaskara does not mention Sankara by name, nor does he mention the name of his philosophy. However by reviewing his arguments against the monistic doctrine of maya and the Advaitic concept of anirvacaniya, it is obvious who and what he is alluding to.
Bhaskara is positively vitriolic when writing about the Advaitin’s concept of maya, referring to it’s adherents as bauddha-matavalambin (those that cling to Buddhist ideology) and goes on to say that their philosophy reeks of Buddhism (bauddha-gandhin). Bhaskara concludes that, “No one but a drunkard could hold such theories” and that Mayavada is subversive of all sastrika knowledge:
vigitam vicchinna-mulam mahayanika-bauddhagathitam mayavadam vyavarnayanto lokan vyamohayanti
Expanding on the contradictory and baseless philosophy of maya propagated by the Mahayanika Buddhists, the Mayavadis have misled the whole world. (Bhaskara’s Brahma-sutra-bhasya 1.4.25)
In his Siddha-traya, the Vaisnava philosopher Yamunacarya (917–1042 CE) stated that Buddhism and Mayavada was essentially the same thing. The only difference he could see was that while one was openly Buddhist (prakata-saugata), the other was simply covered (pracchana-saugata).
Following on from Yamunacarya, his disciple Sri Ramanuja (1017-1137 CE) also concurred that Mayavada was another form of Buddhism. In his Sri Bhashya commentary on the Vedanta-sutras, Ramanuja says that to claim that non-differentiated consciousness is real and all else is false is the same as the Buddhist concept of universal void. Furthermore, Ramanuja states that the concepts of such crypto-Buddhists make a mockery of the teachings of the Vedas (veda-vadacchadma pracchana-bauddha).
Another acarya in the line of Ramanuja, Vedanta Desika (1269–1370) wrote his famous Sata-dusini, a text expounding one hundred flaws found in Mayavada. In that work he refers to Sankara as a rahu-mimamsaka (one who obscures the true meaning of Vedanta), a bhrama-bhiksu (a confused beggar), a cadmavesa-dhari – one who is disguised in false garb, and goes on to assert that, “By memorizing the arguments of the Sata-dusini like a parrot, one would be victorious over the crypto-Buddhists.”
In another work, Paramata-bhangam, Vedanta Desika refers to Sankara as, “One who studied the Vedas in the shop of a Madhyamika Buddhist” (referring to Sankara’s param-guru Gaudapada of whom we will speak of later in this article).
Later philosophers also declared Mayavada to be crypto-Buddhism. The Sankhya philosopher Vijnana-bhiksu (1550–1600 CE) tried to reconcile Vedanta with Sankhya philosophy and synthesize all theistic schools of Indian thought into a philosophy that he called Avibhagadvaita (indistinguishable non-dualism). He was an impartial writer who analyzed both the merits and problems of the various doctrines that he encountered. Concerning Sankara’s philosophy, Vijnana-bhiksu states in his Sankhya Pravacana Bhasya:
brahma-mimamsayam kenapi sutrenavidya-matrato bandhasyanuktatat. avibhago vacanaditya-sutrair-brahma-mimamsaya abhipretas-yavibhaga-laksanadraitasy-avidyadivastavatve’pyavirodhaccha. yat tu vedanta-bruvanamadhunikasya mayavadas-yatra lingam drsyate tat tesamapi vijnanavadyeka-desitaya yuktameva.
There is not a single Brahma-sutra in which bondage is declared to be a mere deception. As to the novel theory of maya propounded by vedanta-bruva (those who claim to be Vedantists), it is only another type of Buddhist of the Vijnanavada school (vijnana-vadyekadesin). This theory has nothing to do with Vedanta and it should be understood that this doctrine of these new Buddhists, who assert the theory of maya and reduce our bondage to mere illusion is in this way refuted. (Sankhya Pravacana Bhasya 1.22)
Later on in his work, Vijnana-bhiksu also quotes the famous verse from Padma Purana (mayavadam asat-chastram). Vijnana-bhiksu considered Buddhism to be nastikavada, or atheism, as it was opposed to Vedic thought. Thus, in effect, he was declaring Mayavadis to be out and out atheists.
Amongst all acaryas and philosophers, Sri Madhvacarya was certainly the most hostile towards Sankara. Throughout his campaign to establish his philosophy of Dvaitavada, Madhva continuously attacked Mayavada, which he considered to be the worst kind of heresy. In his Anu-vyakhyana, Brhad-bhasya and Tattvodyota, Madhva also makes the claim that the Advaitins are crypto-Buddhists – na ca sunyavadinah sakasad vailaksanyam mayavadinah (there is no doctrinal difference between Buddhism and Mayavada). He even quotes Buddhist texts and compares them to Advaitin works to prove his point.