Tens of thousands of people protested in Madrid to oppose any concessions by the government to Catalan pro-independence parties and to call for early elections.
The opposition centre-right and far-right parties called the rally, seeking to make a show of force against Mr Sanchez by capitalising on anger with Catalonia’s separatist leaders and the government’s efforts to establish a dialogue with them.
The government’s proposal last Tuesday to appoint a rapporteur in talks among political parties to address the Catalan independence crisis galvanised the opposition, which deemed it a betrayal and a surrender to pressure from Catalan.
“The time of Sanchez’s government has ended,” Popular Party leader Pablo Casado said before the protest.
Some banners at the rally read “Sanchez, liar” and “Spain is not negotiable and cannot be sold”.
Mr Sanchez, who replaced a conservative government last June in a vote of confidence, holds just a quarter of the seats in parliament and relies on backing from anti-austerity party Podemos, Catalan nationalists and other small parties to pass laws.
The government is squeezed on both sides of the Catalan issue: Deputy Prime Minister Carmen Calvo said on Friday the talks were on track to fail because Catalan pro-independence groups had rejected the government’s proposed framework.