WILLIAM BRANGHAM: As most Western countries tighten their borders, Spain's left-wing Prime Minister Pedro Sanchez has enacted a plan aimed at giving legal status to undocumented immigrants.

It's called regularization.

But late last month, when tens of thousands of migrants tried to illegally cross into the Spanish territory of Ceuta, which borders Morocco, that incident put Spain's immigration policy under the microscope.

Stephanie Sy has more.

STEPHANIE SY: Before most of Madrid wakes up, Carlos Aroca is already at work.

For hours each morning, he collects garbage in one of Europe's busiest capitals.

It's essential work done by an invisible worker.

CARLOS AROCA, Ecuadorian Migrant (through translator): We can work in jobs that many people no longer want to do, jobs in cleaning, fruit picking, farmwork, eldercare, and construction.

STEPHANIE SY: It wasn't his dream job either.

Aroca came to Spain from Ecuador to pursue an MBA.

After a year of study, he lost his legal status and was forced to find jobs willing to hire undocumented immigrants.

CARLOS AROCA (through translator): When it comes to working irregularly, it does hit us pretty hard since we don't have the benefits that the law provides a regular job.

They're not going to pay us the same as someone who's on contract.

STEPHANIE SY: Carlos is among an estimated 600,000 undocumented migrants that now have the opportunity to come out of the shadows.

The royal decree he approved in April provides temporary and renewable legal status to undocumented immigrants who have lived in Spain for the last five months and have no criminal record.

VLADIMIR REVELO, President, Asociacion Ruminahui (through translator): These more than one million immigrants were working.

But they were working in the informal sector.

What this regularization has done is bring them into the formal system so they can now make contributions and have Social Security, access to public health care.

STEPHANIE SY: Vladimir Revelo is the president of a migrant advocacy group in Spain.

The nonprofit has spent decades helping migrants navigate the immigration system.

He's helped Aroca and hundreds of people like him, who are working, paying rent and raising families, but unable to fully participate in the country many now consider home.

CARLOS AROCA (through translator): My first reaction was one of doubt.

I couldn't get my hopes up too much.

Once the law was passed, of course, you could say it was a dream come true.

STEPHANIE SY: Today, foreign workers make up roughly one of every six workers in Spain.

Revelo says the reforms are a pragmatic response to Spain's economic challenges, an aging population, low birth rates and persistent labor shortages.

VLADIMIR REVELO (through translator): Spain and the European Union will need around 60 million workers by 2050 because they need to collect Social Security contributions to maintain pensions for native citizens.

Spanish businesses need this work force.

Without this work force, the construction service and hospitality sectors, as well as the agricultural and parcel delivery sectors, would grind to a halt.

STEPHANIE SY: But not everyone sees the policy as an economic necessity.

Opposition leader Alberto Nunez Feijoo argues Spain lacks the housing, public services and infrastructure to absorb more migrants.

ALBERTO NUNEZ FEIJOO, President, Popular Party (through translator): This regularization has harmful consequences for Spain and therefore for all of Europe, because it will put pressure on public services, further strain the housing market, and create problems in the community.

STEPHANIE SY: And, last month, the immigration debate exploded overnight.

More than 350 miles south of Madrid, Spain's tiny North African territory of Ceuta was confronted with a wave of people.

Tens of thousands of migrants attempted to cross into Ceuta from neighboring Morocco.

The chaotic scenes quickly spread across TV screens and social media, families sleeping on beaches, people washing clothes in the sea and lining up for aid.

More than 100 people died, either drowning or crushed by the crowd.

For many who thought they'd made it, the crossing represented years of hope distilled into a single desperate attempt.

AHMED HAROUN, Sudanese Migrant: I have many dreams.

And the first dreams to me, just I want to help my lost family.

Why I said lost?

Because I lost a lot of them, and I will fight for them.

I will fight.

I will do anything just to have them.

STEPHANIE SY: Twenty-nine-year-old Ahmed Haroun says he waited four years for the opportunity to escape Darfur, Sudan.

AHMED HAROUN: No, I'm not scared of this life.

I believe everyone here just die one time.

No one can die two times.

STEPHANIE SY: But most migrants who entered Ceuta have since been deported back to Morocco or returned on their own.

What led to the mass attempt to cross into Spanish territory is unclear.

But experts say it was likely not spontaneous.

JEREMY KONYNDYK, President, Refugees International: There was misinformation circulating on social media in Morocco, telling people that they could go to Spain and that they would have a chance to go there and stay.

STEPHANIE SY: Jeremy Konyndyk is the president of Refugees International.

He said the role Morocco played in the chaos deserves scrutiny.

JEREMY KONYNDYK: What we do know pretty definitively is that the Moroccan border guards who would normally have prevented something like this did not obstruct it.

This was a breakdown, potentially a willful breakdown, by the Moroccan government in their border controls, perhaps to put some kind of pressure on Spain, because they knew that there would be this kind of hysteria in Europe over these sorts of images.

STEPHANIE SY: The images gave anti-immigration voices fuel to criticize Spain's immigration reforms, even though Spain has long taken a hard line on the kind of irregular migration that occurred in Ceuta.

Spain's far right party President Santiago Abascal reacted.

SANTIAGO ABASCAL, Vox Party Leader (through translator): We are facing an invasion, and it must be called that.

I think that at this point no one can deny that the arrival of 65,000 people, according to what's being said at the moment, is an invasion.

And we are facing an act of war promoted by Morocco and tolerated and allowed by Pedro Sanchez.

STEPHANIE SY: Twenty-two European Union member states led by Italy and Denmark warned that large-scale regularization programs risk drawing more migrants to Europe.

JEREMY KONYNDYK: The far right immigration narrative in Europe has always been that Europe is going to be overrun by people from around the world if they open their doors and if they treat migrants humanely.

And so, for them, they want to spin this as definitive proof of that.

STEPHANIE SY: Konyndyk says far right anti-migrant sentiment undermines the economic solution that he says more migration offers and that Europe needs.

JEREMY KONYNDYK: They have created for themselves an impossible situation, where their economy desperately needs migration, and their politics will not allow for it.

What we see the Sanchez government doing here in Spain is trying for a more sane and rational migration policy that actually reflects the realities of their country and their economy.

STEPHANIE SY: Carlos Aroca says he's looking forward to having more personal stability and returning to his original dream of working in business.

Carlos, what is your message to people who don't agree with these immigration reforms?

CARLOS AROCA (through translator): We migrants in most cases leave our countries in search of a better life.

What we come here to do is to contribute to the country that welcomes us.

We want to be able to fit into an environment of coexistence through our work and our culture, respecting the traditions they have, but also contributing our own, which are also very valuable.

STEPHANIE SY: For the "PBS News Hour," I'm Stephanie Sy.