(CNN) For years it was a rite of passage for European holidaymakers visiting another country on the continent -- the dreaded phone bill on the return home.

No sooner had tans from skiing in France or beaching in Spain faded than Europeans were hit with eye-watering roaming charges for every call, text and Google search.

Then suddenly the roaming charges vanished, almost as if by magic. Europeans could skip across borders with the same mobile phone allowances and fees they enjoyed at home.

Behind the scrapping of roaming charges in June 2017 lay a tortuous, decade-long struggle by the European Parliament.

Yet how many of European Union's 500 million citizens realize this far-reaching legislation -- called "roam like at home" -- was partly down to their local Member of European Parliament (MEP) is debatable.

As the European Parliament elections near -- between May 23 and May 26 -- one of the biggest challenges facing MEPs is communicating to voters what they actually do.

Even experts who have spent their entire careers studying the European Parliament admit it's a complex institution for voters to get to grips with.

From rules on how many hours employees work, to the quality of the air they breathe and even data privacy, the European Parliament passes hundreds of laws each year affecting 500 million people. Not to mention approving EU budgets and appointing the President of the European Commission.

Euroskeptics meanwhile, argue the Parliament doesn't really exert that much power, instead tinkering on the edges of legislation that must first be proposed by the European Commission anyway.

If you want a better idea of how the European Parliament shapes laws, phone roaming charges are a pretty good place to start.

All for one

The Parliament is one of three institutions that must come together in agreement to pass a law -- the others being the European Commission and Council of the European Union.

The Parliament -- made up of 751 MEPs elected by citizens -- is seen as the body representing the voice of the people. It has the power to amend, reject and approve legislation, alongside the Council, but not the power to propose a law in the first place -- only the Commission can do that.

"The Commission is the most important institution in this area," said Auke Willems, a fellow of EU law at the London School of Economics. "It ultimately operates as an agent hanging over the two institutions, making a compromise."

But that doesn't mean the Parliament isn't a crucial part of the lawmaking process. Where it "really gains power," said Willems, is by "proposing amendments that go to the Council."

That's where the bargaining with the Council -- which is made up of government ministers from the 28 member states -- comes in, ultimately leading to a compromise. Once there's agreement, all three bodies sign it off.

How long all this takes depends on the gravity of the law. The majority of laws get passed in what is called the "first reading," which is roughly within a year, according to Willems.

In the case of "roam like at home," the Commission first made the proposal in 2006 and it was rejected and amended and gradually implemented over a decade. In 2007 charges were reduced by 60% and by 2017 they were scrapped entirely.

This is the formal process for passing laws. But there's also an informal law-making process called "trilogues" -- essentially a tri-party meeting between the Commission, Council and Parliament -- that pass an estimated 80% of laws, according to Willems.

Trilogues are efficient -- the vast majority of legislation gets passed in the first reading, said Willems. But he added that they are also "shrouded in secrecy" as the institutions don't publish details of what takes place.

Whether it be a formal setting or trilogues, it's still up to the Commission to propose laws in the first place. According to Gawain Towler, spokesman for the Brexit Party and former UKIP aide who worked in the European Parliament for a decade, this means the Parliament "doesn't actually have much power."

He called it a "vaguely democratic fig leaf on a regulatory machine, tinkering at the edges of legislation."

'I couldn't have done it without MEPs'

Meanwhile the former European Commissioner who proposed the "roam like at home" laws, Viviane Reding, said that "without the European Parliament I could never have done it."

She says the idea first came about in 2004, after an increasing number of MEPs said their citizens were complaining of enormous phone bills whenever they went abroad.

The Parliament, which is pro-consumer rights, backed Reding's proposal. The Council, which represents the member states, fought against it.

Timeline 2006: Commission proposes changes 2007: Price cap for calls 2009: Price cap for text messages 2012: Price cap for data 2014: Parliament votes to end roaming charges 2015: Parliament and Council formally adopt end of roaming charges 2016: Roaming charges on calls, text, data are reduced 2017: 'Roam like at Home' becomes reality Source: European Commission

"Because some telecommunication companies belong to the state, their revenue went into the state budget," explained Reding. "So they were all terribly opposed to having roaming charges eliminated."

"I needed the Parliament not only to vote, but to go vocal," said Reding, adding that MEPs went back to their constituencies to push the issue to media and ministers.

"They really put the pressure on."

Towler is more skeptical, acknowledging that the Parliament was involved and signed it off, but ultimately the law "was a Commission thing."

He said that for MEPs who travel to different countries almost weekly, phone roaming was first and foremost "in their own interests," rather than in the interests of citizens who might be able to afford a "two-week holiday" each year.

Apathetic about elections? You're not alone

Do citizens realize the role MEPs played in scrapping phone roaming charges? Reding believes those in some European countries, such as her native Luxembourg, are more aware of European lawmaking than in others such as Brexit-voting Britain.

"There is an enormous disconnect between what the European Union does and the Brits," she said, adding that the reason could lie with the UK media "not explaining enough who makes the decisions."

Willems sees it as a broader PR problem with the EU, saying "it doesn't really sell what it does well, and gets criticized for what it doesn't do well."

One thing is certain: since the first European parliamentary elections in 1979, voter turnout has been steadily dropping. The last election, held in 2014, had a turnout of just 42% -- ranging from 89% in Belgium (the home of the EU headquarters), to just 13% in Slovakia. To put that in perspective, voter turnout in the 2016 US election was 61%.

Part of the disconnect between voters and MEPs can be put down to geography, said Willems, adding that the headquarters in Brussels is removed from most other European capitals.

The way the European Parliament works is also "quite obscure" to voters, he said. Unlike national parliaments, the European Parliament isn't organized by political parties, but political "groupings."

This means a citizen might vote for a national party, only to see them taking a seat in a grouping that includes parties from other countries whose policies they are not in agreement with. For example, German Chancellor Angela Merkel's center-right Christian Democratic Union is in a grouping with Hungarian Prime Minister Viktor Orban's rightwing Fidesz -- parties with vastly different stances on immigration, but still nonetheless part of the European People's Party (EPP) group in European Parliament.

Fidesz joined the EPP in 1996, but in recent years, the parliamentary group has become increasingly concerned about Fidesz' hardline policies under Orban. In March, the EPP suspended Fidesz, though it stopped short of full expulsion.

The parliamentary groupings setup "creates a distance between voters and ultimate outcomes" in the legislative procedure, said Willems.

The distance might be great, but with just days until the European elections, decision time for voters is inching ever closer.