Yes and no. In Congress, all the amendments of totality presented by the groups are voted on together. In the Senate, on the other hand, the vetoes are voted one by one, but it may happen, as in fact already happened in the time of José Luis Rodríguez Zapatero in Moncloa, that the PP supports the proposals of other formations in order to inflict a punishment to the Government. Between 2004 and 2011, the Socialist Executive saw knocked down their Budgets in the Senate on four occasions: in those of 2005 and 2011 the BNG veto was successful; in those of 2008, the partial veto of CiU to the Housing section triumphed, and in those of 2009 ERC no.
How is the Senate made up today? It seats 265 honorable members, for which the absolute majority stands at 133 votes. The PSOE has 114 seats. It is followed by the PP (100), the ERC-EH Bildu group (16), PNV (10), Izquierda Confederal (Adelante Andalucía, Compromís, Més per Mallorca, Geroa Bai, Más Madrid and Agrupación Socialista Gomera), with 6; Junts-Coalición Canaria (6), Ciudadanos-Teruel Existe-PRC (6) and Mixed (Vox, PAR, UPN and two former independent Cs), with 7. Socialists and PNV add 124 senators, and they would need nine more to reach an absolute majority. In the upper house, the PSOE has several lordships from like-minded parties, but it does not have United We Can, because it was left without representation. Adding Compromís (1), Más Madrid (1), ASG (1), Teruel Existe (2), PRC (1) and Partido Aragonés (1) would reach 131.
ERC has 14 own senators (The other two from his group are provided by Bildu, who last week supported the Budgets but who also feels concerned by the linguistic issue). The 100 parliamentarians of the PP could join him, plus JxCat-CC (6), Cs (3), Vox (3), the two independents and UPN (1). It would be 129, or 131 if the two from Bildu are added. The key is therefore held by Adelante Andalucía, Més and Geroa Bai. Three seats that can tip the balance.
Arithmetically, the front of the is not possible, but politically it is not so simple build that alliance.