So, you're worried you're being underpaid.

Maybe it's because your mates are earning more for doing the same job.

Or because you worked the weekend and you were only paid a flat rate.

Here's our definitive guide on what to do.

First, check out what you're meant to be paid.

Jump onto the Fair Work Ombudsman's website and punch your details into the free pay calculator.

You'll have to provide some information like how old you are and if you're an apprentice.

Once you're done, it'll tell you exactly how much you should be earning per hour, per week and for every night or weekend.

There's also a pay checker tool that's been put together by a new union group called Hospo Voice, which is geared towards the smartphone generation.

A new online-based union called Hospo Voice has been started for hospitality workers. ( ABC Mildura-Swan Hill: Kellie Hollingworth )

Hospo Voice has been started by the United Voice union, which has traditionally covered the hospitality sector.

"We're doing that because really the current model offered by the union movement in Australia is just not working for these young workers," said United Voice's secretary Jess Walsh.

The union will offer its services exclusively online, including the pay checker, a place to record their hours and a harassment diary.

"We know that how young workers access the world is through their devices and that's how we wanted to reach out to them.

"We also wanted to make it affordable. So this is as far as we know the first Netflix-style union membership model in Australia where people can join for $9.99 per month with one month free."

Hospo Voice has already had 150 young workers sign up.

Speak to your co-workers

If you find out you're being underpaid, have a chat to the people you're working with.

Keelia Fitzpatrick from the Young Workers Centre is urging people to speak up if they've been underpaid. ( Supplied )

Get together a record of the hours you've been working.

You'll probably want to approach your boss as a group, like some staff at Barry Cafe in Northcote did recently.

"We always say that there's power in numbers, you shouldn't go to meetings alone with an employer," says Keelia Fitzpatrick, the coordinator of the Young Workers Centre in Melbourne.

Ms Walsh said if one person's being underpaid, it's likely that others are as well.

"I think young workers know that if they just take it on by themselves, they're going to be vulnerable," she said.

"If they have everyone else with them they're going to be powerful and again that's what Hospo Voice is trying to do. To bring young workers who currently feel disposable and isolated together."

What do I say to my boss?

Keep it simple, says Ms Fitzpatrick.

"You say that you went on the Fair Work Ombudsman's site and got some information about the minimum rate you should be paid for working in your industry," she said.

Afterwards, put everything in writing, including your questions to your boss and a request that they resolve the issue informally.

Let's say it was all one big mistake and your boss is sorry.

If that's the case, you should be receiving back pay either in one lump sum or over the course of a few months.

Hospo Voice has produced template letters that you can send to your boss and begin to create that necessary paper trail.

What if my boss refuses to do anything about it?

This is where it gets tricky. You need to escalate the problem.

The Fair Work Commission can help if you're fired unfairly. ( ABC News )

Take your paper trail, including your email to your boss and the hours you've been working, and go to the Fair Work Ombudsman or the hospitality union, United Voice.

If you're in Victoria, you can contact the Young Workers Centre.

"Often an employer is more likely to respond to a letter or an email from one of those bodies, rather than from one of their workers, unfortunately," Ms Fitzpatrick says.

My boss has docked my shifts/fired me. Help.

This happens often, but it's potentially illegal.

"It's actually unlawful for an employer to dismiss someone, or to refuse to hire someone, or to take away shifts simply because someone has asked about a workplace right," Ms Fitzpatrick says.

If this happens to you, you have to file what's called a General Protections Dismissal claim, which puts your boss on notice.

You do this through the Fair Work Commission but there's a limited timeframe.

You have to do this within 21 days.

"Once you've filed your form with the Fair Work Commission, it will be sent to your employer, who is required to respond to the allegations and put their side forward," she said.

"It will then go to a conciliation through the Fair Work Commission where we try to resolve it."

Does this mean I'll get my job back?

Maybe, but probably not.

"Often it's about coming to a settlement figure with the employer, which doesn't involve reinstatement. It involves money to cover the loss of wages that you've had since you lost the job," Ms Fitzpatrick says.

How long will it take to get my money?

It depends, but anywhere from a few weeks to more than a year.

Some hospitality workers have been raising concerns about being paid at below-award rates. ( unsplash.com )

Sometimes the businesses that get letters from unions or legal centres decide to fix the problem quickly, but others can draw the process out.

"Don't expect to get the money overnight," Ms Fitzpatrick says.

"Strap in for a long-winded process that can involve lots of letters."

If you do get your money back, but you were being paid cash in hand, you might get a visit from the tax man.

"Generally the tax office is not going after quite small amounts of money that young people haven't been upfront about," Ms Fitzpatrick says.

"You may be facing probably small consequences from the tax office."

If I have to wait for so that long, is it really worth it?

According to Ms Fitzpatrick, it definitely is.

"Don't be discouraged by the formalities and the waiting period," she says.

"This is money that you are rightfully entitled to under law.

"The more people that stand up for the money that they're owed and the more people that stand up against wage theft, the more employers are going to realise that they can no longer get away with it."

I'm angry. How did things get so bad?

That's a question that keeps Jess Walsh from United Voice up at night.

"Wage theft has become a business model in hospitality," she said.

"What employers do is they try and get away with underpaying people and see if they get caught and get taken to court, which is quite a long and prohibitive process."

The unions want bosses who underpay their staff to be criminally charged. ( ABC: Xavier La Canna )

She's calling for the system to be overhauled and the underpayment of workers to be criminalised.

"I think the first time a high profile employer actually has charges brought against them, that is what is going to be really powerful in changing employer behaviour in hospitality."

But according to the union, the tide is turning and young workers are fighting back.

"We've had a string of high-profile venues that have been exposed as treating their staff poorly and underpaying them," she said.

"And I think young hospitality workers are really starting to turn the tables in the industry."