The centre-right Ciudadanos party, which was born out of opposition to Catalan separatism, held a rally in front of Catalonia's regional government headquarters in Barcelona under the slogan: “That's enough! Justice and coexistence”.
After the rally, Ciudadanos leader Alberto Rivera tweeted a video of his speech, in which he celebrated the union.
“We have had enough of seeing how radicals roam freely and scare millions of Spaniards on their land. The streets belong to everyone,” he tweeted before the rally began.
Rivera has called on Sanchez to suspend Catalonia's autonomy just as the central government did in 2017 after the Catalan parliament declared independence following a banned secession referendum.
The streets of Barcelona and other Catalan cities have been rocked by protests since Spain's Supreme Court sentenced nine separatist leaders, many of them former regional government ministers, last Monday to jail terms of up to 13 years for sedition over the failed 2017 independence bid.
Nearly 600 people have been injured in clashes with police since the protests started. A police officer was in “very serious condition” and a demonstrator was in “critical condition” according to Barcelona mayor Ada Colau.
In an interview published in top-selling daily newspaper El Pais, the leader of the main conservative opposition Popular Party (PP), Pablo Casado, accused the government of “pretending nothing has happened” and promising that everything will return to normal “with moderation”.
“There can be no dialogue with those who make Catalonia burn,” he said in reference to Catalonia's separatist president Quim Torra who on Saturday called for “unconditional” negotiations with Sanchez.
That appeared to be aimed at ensuring that a legal referendum on independence, currently a non-starter for Madrid, was up for discussion.
Sanchez, who came to power in June 2018 with the support of Catalan separatist parties, refused to meet with Torra until he “clearly” condemns this week's violence and recognises that half of Catalonia's roughly 7.5 million residents do not want independence.
A poll published in July by a public Catalan institute showed support for an independent Catalonia at its lowest level in two years, with 48.3 percent of people against and 44 percent in favour.
The court's decision has thrust the Catalan dispute to the heart of the political debate ahead of Spain's November 10 general election, its fourth in as many years.
According to the first poll since Monday's verdict, the ruling Socialists are likely to secure the most votes but again fall short of a majority. The PP was tipped to make significant gains.
Published by the daily El Mundo, the survey predicted Sanchez's Socialists would capture 122 seats in the 350-seat parliament, slightly down from 123 it took in the last election in April, while the PP would win 98 seats, up from 66.
“Order and territory has never been a winning bet for the Socialists,” Pablo Simon, a political science professor at Madrid's Carlos III university, wrote in a blog post on Saturday, adding the Catalan crisis will “increase polarisation” which would benefit parties with more extreme positions like the far-right Vox and radical separatists CUP.
Barcelona returned to relative calm Saturday night after six days of demonstrations against the jailing of separatist leaders.
But on iconic Las Ramblas street, protesters set up barricades and lit fires before they were dispersed by police firing foam projectiles.
Overnight Friday, radical separatists had hurled rocks and fireworks at police who responded with tear gas and rubber bullets.