AFL-CIO President Richard Trumka called Republican nominee Donald Trump the most racist presidential candidate ever Monday in an appeal to Latino voters.

Trump has made immigration a cornerstone of his presidential campaign. His promise to be tough on illegal immigrants and border security has gained him many supporters and critics. Trumka argued in an opinion piece that the policies show the nominee is racist and xenophobic and that Latinos are key to defeating him.

“There is a lot at stake at this election for all working people across America,” Trumka wrote for the Spanish-Language news service Univision. “But Latino families have the most to lose if Donald Trump gets elected. They also have the power to stop the most xenophobic and racist presidential candidate that our nation has ever seen.”

Trump has focused on immigration throughout his campaign. He has promised to enforce border security and has proposed travel restrictions for regions known for Islamic extremism. He has also promised to deport immigrants already here illegally.

Trump has been accused by critics of being racist against people with Latino backgrounds. He has focused on Mexico in his pitch for better border security. Roughly half of all illegal immigrants come from Mexico, according to a 2014 study by the Pew Research Center.

“From the beginning Trump has based his campaign on attacking Latino working families,” Trumka said. “He wants to separate hardworking immigrant families by deporting our friends, neighbors, and coworkers. His most prominent campaign promise is to build a wall that will further separate and alienate Latino immigrant families.”

The AFL-CIO is the largest coalition of labor unions in the country at roughly 12.5 million members. The union has already used its vast political influence to convince voters Trump would be dangerous for workers. Its Latino-targeted campaign comes as the Republican nominee lags by 50 points among Latino voters, according to a recent poll.

“Trump is a double threat to hardworking Latino families, not only because of his inhumane and senseless immigration proposals,” Trumka said. “Trump has clearly stated that he does not support raising wages, even as thousands of Latino families in the nation would benefit greatly from a pay increase.”

The AFL-CIO has also issued personal attacks against Trump in an attempt to undermine his character. The union declared him its loser of the week several times throughout the election. Trumka also accused Trump of trying to divide immigrant families Jan. 4.

The AFL-CIO has joined other groups to campaign against Trump. The union joined forces May 12 with other unions and environmentalist Tom Steyer to launch the For Our Future PAC. The political fund has focused on the grassroots level to garner support through community organizing.

The AFL-CIO is not alone, as many other unions relentlessly attack the business mogul. The United Auto Workers (UAW) has organized demonstrations against the presidential hopeful during his rallies and speeches. The American Postal Workers Union (APWU) accused him of attempting to incite racial division.

Trump has been able to win over some within the labor movement. The National Border Patrol Council (NBPC) made its first-ever presidential endorsement March 30 in favor of the outspoken candidate. A modest list of other unions has also endorsed him.