Four bicycle couriers are taking their companies to a tribunal in a bid to get employed workers' rights, including paid holidays and the minimum wage.
If successful, the case could have a huge impact on the growing number of workers who are being wrongly categorised as self-employed.
The couriers are considered self-employed contractors despite working for one firm for about 50 hours a week.
The courier companies say the tribunal claims are unfounded.
The often-long working day of a London courier involves weaving through the city's crowded and congested streets in the saddle covering 60 to 70 miles, to be normally paid between £2 and £3 per delivery, depending on distance.
At the employment tribunal, the four London couriers will seek a declaration that they are either "employed" or "workers", which would entitle them to benefits and rights.
Among them is Andrew Boxer, who works for Excel. "I am typical," he said. "I work for one company for around 50 hours a week. They tell me what to do, when to do it and how to do it.
"I am monitored, have to have company ID with me at all times, and can't take work from other companies.
"I get paid per delivery, not per hour. I am required to sign a contract which says that I am self-employed, which means I don't get any employment rights."
Excel responded, saying: "Within the London market, couriers operate as independent sub-contractors and I am confident that any tribunal will uphold this view."
Another courier, Mario Gbobo, fell off his bike and was left with a long and nasty scar on his arm.
"The parcel I was carrying was insured, but I wasn't," he said. "Someone came and collected the parcel. I had to fend for myself and ended up returning to work before the injury healed because I needed the money."
The couriers are taking Excel, as well as City Sprint, Addison Lee and eCourier, to an employment tribunal with the support of their union, the Independent Workers Union of Great Britain.
The union's president, Jason Moyer-Lee, said: "Employers are taking advantage of the power imbalance and forcing the couriers to accept a job with zero employment rights.
"The couriers should be like all other workers and have the right to the minimum wage and paid holidays, among other things."
If the tribunal supports their view, it could prove to be a landmark case.
An estimated 4.8 million people in the UK are self-employed, and the TUC said it has seen a growing number of industries, from hairdressing to food production, choosing to categorise workers as self-employed.
However, a survey by Citizens Advice last August suggested that as many as 460,000 people could be "bogusly self-employed", and therefore would be missing out on all of the rights that an employed person is entitled to.
The barrister representing the couriers, Jason Galbraith-Marten QC, believes their case could have a significant impact on the modern labour market.
"Couriers have been told that they are self-employed and they are put on contracts that describe them as self-employed," he said.
"A win for them would mean that a court had looked at the true circumstances under which they are working, and decided that they are not truly self-employed.
"And that means others in similar circumstances can go to a court and say, 'it doesn't matter what it says on the contract, I am in fact a worker and can I have the same rights?" he added.
City Sprint said it believed the assertions regarding the employment status of their courier fleet were "unfounded".
"We're very proud of our fleet and offer them the opportunity to achieve among the highest earnings in the industry," a spokesman said.
Addison Lee said it would not comment on this ongoing litigation, and eCourier said it has not been legally notified from the tribunal about any claim for fairer work contracts.
What kinds of employment status exist?
They benefit from the highest level of employment protection. There must be a contract between the employee and employer requiring the employee to carry out duties personally, meaning they cannot send someone else to carry out their work. The employee must also be under the control of the employer in terms of hours, working practices and workplace rules, and be sufficiently integrated into the workplace.
Rights and benefits include holiday pay, national minimum wage, rest breaks, discrimination protection, whistleblowing, deduction from wages, pension contribution from an employer under auto-enrolment, a written contract of employment, unfair dismissal protection, redundancy payment, statutory minimum notice pay, maternity/paternity pay, paid time off for antenatal appointments and a right to request flexible working.
They hold an intermediate position between employees and the self-employed. There must be a contract between the worker and employer requiring the worker to carry out duties personally but the worker is not integrated or subject to as much control as an employee. If the "employer" is actually a client or customer of any business carried on by the individual, they will not be a worker, but will instead be self-employed.
Rights and benefits include holiday pay, national minimum wage, rest breaks, discrimination protection, whistleblowing, deduction from wages and pension contribution from employer under auto-enrolment.
This status carries the least legal protection. There will be a contract but there is no requirement that the self-employed worker carries out the service personally. The self-employed usually enjoy maximum freedom as to how to deliver the service and are not subject to workplace rules.
Rights tend to be governed by the contract rather than any statutory rights.
Source: Cloisters barristers chambers