On his return, de los Reyes quickly set about to launching several initiatives that he already had in mind while still in Spain. On October 25, 1901, ten days after he returned to Manila, he sought authority from the Philippine Commission to publish his
Defensor de Filipinas, which was refused. On October 31, he appeared before the commission, with
Pedro Paterno and
Pascual H. Poblete to seek permission to form a political party, the
Partido Nacionalista, which was also denied. He wanted to push for a party that would push for independence within the framework of US occupation. Eventually, Poblete persistently managed to form the short-lived Partido Nacionalista (predecessor of the
Nacionalista Party), which de los Reyes had also joined. He was eventually named its leader. The
Union Democratica de Litografos, Impresores, Encuadernadores y Otros Obreros was thus formed, which came to be known as the
labor union federation Union Obrera Democratica (UOD) on February 2, 1902. De los Reyes was its first president. De los Reyes took home with him works by socialists such as
Karl Marx, Proudhon, Bakunin, and
Errico Malatesta. Malatesta's
Propaganda socialista fra contadini was particularly familiar to union organizers. The UOD was the first labor union federation in the Philippines, soon being joined by neighborhood associations from
Cavite,
Quiapo,
Santa Cruz and
Sampaloc; company guilds from the
San Miguel Brewery and L.R. Yangco Shipping Company; and trade associations of printers,
tabaqueros, tailors, sculptors, seamen, and cooks. At its peak in 1903, the UOD's membership was estimated at twenty thousand. As conceived by de los Reyes, the UOD's aim was to "achieve the longed-for alliance between capital and labor" by bringing together workers and employers in a spirit of friendship, mutual respect, and recognized interdependence. De los Reyes also wished to enlighten the masses as a prerequisite to modern nationhood. In this end, he organized
veladas instructivo-recreativas as a way to "improve themselves and learn the life of cultured peoples". He had observed that workers in Europe had clubs and cafes where they could read newspapers and discuss current events, and wished to emulate that in the Philippines. De los Reyes also published the UOD's official organ,
La Redencion del Obrero. De los Reyes spent this time mediating in labor disputes and other union-organizing activities. The press at this time called him a "Malay Lerroux" and compared him to Spanish labor leader
Pablo Iglesias. On August 17, 1902, he was arrested on the trumped-up charge that he gave orders to assassinate scabs in a strike at the Commercial Tobacco Factory. De los Reyes was eventually released on January 30, 1903, by Governor
William Howard Taft, stating that the statute "was not in line with current American thinking on the subject" and was given the condition that he would henceforth shy away from labor organizations. While in prison, de los Reyes tendered his resignation from the UOD on September 14, 1902, and was later replaced by Dominador Gómez. After leaving the UOD, de los Reyes tried to patch up internal rivalries within the organization but ultimately failed. The UOD was dissolved and in its place was the
Unión del Trabajo de Filipinas, headed by writer
Lope K. Santos. After this, de los Reyes focused on his
Redencion del Obrero while contributing to papers like
El Comercio,
Grito del Pueblo, and others. He took up causes such as labor rights, universal suffrage, the exclusion of Chinese immigrant labor, and parity of Filipinos and Americans in the civil service. The right of women to suffrage was an important advocacy of Isabelo during his adult life. ==Japan, Hong Kong, and return to Spain==