​​​​​​​BOGOTA, Colombia

President Gustavo Petro urged Colombians to mobilize on International Labor Day to support a referendum on health and labor reforms, following setbacks for his initiatives in Congress.

The reforms, key components of his administration's proposed social transformation package, have faced significant opposition in the Senate, where they were recently defeated.

Petro, Colombia's first leftist president, is leveraging May Day commemorations to advance campaign promises that have yet to be realized.

"Let the people speak. Tomorrow we will fight for the referendum. The Constitution states that sovereignty resides exclusively in the people, not in any monarch. Tomorrow, we want thousands of Colombians in the streets," he said Wednesday, rallying citizens to march in support of his proposals.

The president wants to generate widespread support for a 12-question referendum designed to improve working conditions, which he intends to formally present to the Senate after addressing thousands of marchers at Bogota's iconic Plaza de Bolívar.

The Senate will then have 30 days to vote on the referendum's approval. If approved, Colombians will vote on the questions in a referendum scheduled in September or October.

More than 13.5 million affirmative votes are required for the referendum to be binding. Should the threshold be met and a majority vote achieved, the questions must then be enacted as laws, decrees or resolutions.

The government, however, faces a challenging path, lacking a majority in Congress.

Thursday's march is critical to exert pressure on undecided lawmakers to vote in favor of the referendum.

To ensure a substantial turnout, Petro has mobilized labor unions and 23,000 indigenous people who arrived earlier this week in Bogota from southern Colombia.