The anti-government protest was the third in a week, and came days after the socialist president declared a state of emergency in the economically struggling country. He gave himself decree powers for 60 days.
Thousands of people turned out for the march in downtown Caracas, but police blocked the route. A small group tried to break through and was turned back by tear gas.
On Tuesday, opposition leader Henrique Capriles called on the country to reject the extra powers granted Maduro.
Venezuela has seen constant small-scale protests in recent weeks against widespread water and electricity cuts.
Also Read
The opposition roiled the country with bloody nationwide protests in 2014, but protests have tended to be small and peaceful since then.
A majority of the country wants Maduro out, according to opinion polls. Venezuelans overwhelmingly voted for the opposition in congressional elections in December, but state institutions have blocked the opposition-controlled congress from passing any legislation.
With congress unable to push through legislation, opposition leaders have begun turning their attention to the streets and the recall referendum as their best option to exert political pressure.
Yesterday, Almagro called that claim absurd and said he would not be threatened. "I am not a CIA agent. And your lie, even if it is repeated a thousand times, will never be true," he wrote in an open letter to Maduro.