"This is not the constitution of my country," they yelled, referring to a recently approved constitutional amendment that allows for private property along coasts and rivers.
One man spread several towels on the asphalt road and lay down. Another set up an inflatable palm tree.
"The beaches belong to the people, not to businessmen," the protesters chanted.
One of the Caribbean country's biggest attractions is its white-sand beaches and turquoise waters along its eastern coast, which is peppered with dozens of celebrity homes and exclusive resorts.
Legislator Minou Tavarez Mirabal went outside to talk with them. "These kind of protests are to let us know that citizens are watching us," she said.
People also have spoken out against other constitutional amendments, such as denying citizenship to children of foreigners born in the Dominican Republic and prohibiting abortion even in cases of rape, incest or a health threat to a woman.
President Leonel Fernandez and opposition leader Miguel Vargas Maldonado supported the amendment that guaranteed the right to private property along beaches and rivers, without giving any reasons.