Los Angeles police estimated at least 10,000 people attended the midday rally and march. They said there were no arrests and it was peaceful.
The protesters are demanding Trump release his tax returns to show transparency. The demonstration was held on traditional Tax Day. It started with a rally at Pershing Square then the group marched through the streets to City Hall.
"He works for us and we have a right to see what business conflicts exist in his background," protester Michael Iglesias said.
Congressmen Ted Lieu and Brad Sherman spoke on the steps of City Hall to the large crowd.
"It's time for Donald Trump to stop posing as a representative of the American working class, while trying to shift the tax burden to working families and our children," Sherman said.
The tax law specialist and CPA added Trump could have released his most recent returns despite being audited. Democrats in Congress want the House Ways and Means Committee to vote in favor of Trump making his returns public, but Republicans have rebuffed those efforts.
The demonstration is one of many that happened in California and across the country. There has been no word or reaction from Trump regarding the protests.
In Berkeley, pro- and anti-Trump protesters clashed with reports of fights, property damage and protesters throwing objects such as fireworks. At least 21 people were arrested. It was unclear if the protest was part of the Tax Day marches.