Behind the pristine business attire and impeccable offices, banks in the United States have a secret: Their public faces — tellers and salespeople — are harried working-class people. These bank employees don wide smiles and deliver well-rehearsed pitches in their daily dealings with customers, but they earn low wages, face job instability and contend with demands that make them choose between ethical practices and keeping their jobs.

Now, bank tellers in the United States will ask for the same protections enjoyed by workers across the world: a union — and they're fighting not only to take care of themselves, but also to take care of their customers.

On Tuesday, over 15,000 U.S. bank workers with the Spain-based bank Santander will declare their intent to establish this country's first bank workers' union. They'll deliver petitions, take over corporate lobbies and begin the long struggle to bring collective bargaining to an industry with predatory practices and lots of low-wage workers. And across the world, in European and South American countries with strong banking unions, hundreds of thousands of bank employees are expected to demonstrate in solidarity.

"In every other developed economy in the world, bank worker unions are the backbone of the labor movement," Teresa Casertano, the global campaigns manager for the Committee for Better Banks, which was instrumental in developing the union effort, said in an interview. "They're strong unions with highest union density, and they usual have broad sectoral bargaining so that every bank worker is covered."

Santander is an international bank — employees of the bank in many other countries enjoy collective bargaining rights. Mark Von Holden/AP

The U.S. bank workers have three demands. The first is greater wages and greater share of the profits, and the second is stable, full-time jobs. Crisp uniforms and polished storefronts aside, bank tellers are solidly low-wage employees — and wages have only taken a downturn over the past decade; as of May 2015, the median annual wage for a bank teller was $26,410.

The third demand isn't just about protecting workers or shoring up their jobs — it's about stopping predatory banking practices that pit bank workers against their own communities.

When it comes to consumer banking's more devious practices, like hawking off high-interest loans or subprime auto loans, it's the salespeople and tellers who end up convincing hapless customers to sign on. The pressure on bank salespeople comes in the form of overbearing quotas and benchmarks that they have to meet for fear of losing their jobs. Santander workers wishing to remain anonymous told Mic that this can even mean hourly quotas that don't give salespeople adequate time to explain the fundamental terms of the loans. The victims are often people of color and neighbors in their communities.

So that third demand for the bank workers is an end to the overbearing quotas that perpetuate these exploitative tactics.

On Tuesday, 15,000 workers will present their intent to start a union for bank workers. Manu Fernandez/AP

"These workers are caught between doing what's good for the customers and being able to provide for their families," said Arnise Porter, an organizer with the Communications Workers of America.

Porter has spent the past year working with Santander Consumer USA workers in Dallas, where many of the subprime auto loans are sold. Workers tell Porter that the office has a nepotism problem, with family members being hired or promoted over the qualified or experienced. On Tuesday, she'll join a group of nearly 50 Santander employees in a lobby takeover of the Santander Consumer USA offices.

The Dallas contingent will also deliver so-called neutrality letters asking the bank to respect a fair election for union formation, as delegations of bank workers in New York City and Boston deliver signed petitions making their demands.

The American banker workers won't be alone in their demonstrations.

In other countries like Brazil, banker worker unions are a staple of collective bargaining power and the labor movement. Contraf-Cut, the Brazilian bank workers union that has gone on strike every year since 2004, ended their longest strike ever — of 31 days — in October, winning an annual 8% wage increase and raises in food and childcare allowances.

In countries like Brazil, bank worker strikes are regular methods of obtaining better wages for workers. Yasuyoshi Chiba/Getty Images

And so, the low-wage bank workers of the world will stand in solidarity with Santander employees as they begin their fight Tuesday. In Brazil, over 130,000 bank employees will open their bank branches an hour late, spending that time briefing the nation's bank workers on the American initiative while a rally is held at Santander's corporate headquarters in Brazil.

In Argentina, there will be rolling strikes throughout the banking sector, where different banks will close for a day throughout the week — they'll present similar demands as American workers, and hold marches and rallies. In Italy, Portugal, Spain and Germany, delegations of Santander bank workers will deliver letters of support to European banking officials.

The international support isn't just symbolic. The CBB initially kicked off the union drive at the urging of organizers in São Paulo and other foreign banking unions like UNI Global. The logic is that when international banks are introduced to the U.S. labor force — where labor has been systematically weakened — they want to spread those practices to workers in other countries where those banks do business, the CBB's Casertano said.

Santander workers have three demands, one of which is an end to quotas that force workers to hawk exploitative loans onto customers without being able to properly explain the terms of those loans. Pablo Blazquez Dominguez/Getty Images

"One third of the bank workers in the world work in the United States, so when U.S. banks go into other counties, they want to act the way they act in the U.S. — in a nonunion environment," Casertano said.

The 15,000 workers beginning the unionization process have a long road ahead; they expect resistance from the bank. As one Santander worker, who asked to remain anonymous for fear of retaliation, said in an interview, many front-line employees have decided that internal human resources procedures and relationships with management are dead ends to achieving their basic rights in the workplace.

"We live in fear at Santander, and without a voice," she said. "When we have a union, we will have a voice."