Unpaid internships should be banned to help ensure that thousands of young people do not miss out on jobs in top professions, it has been suggested.
A new report also argues that employers should take into account an applicant's background when hiring, and calls for more to be done to teach teenagers skills like teamwork and confidence that are needed in the workplace.
The All Party Parliamentary Group (APPG) on social mobility, which produced the report, warned that "significant barriers" are preventing less advantaged youngsters for gaining jobs in leading professions like the law, journalism and medicine, and more needs to be done to tackle the issue.
It says that firms should use "contextual recruitment" - looking at what a job candidate has achieved given their background, for example if they came from a disadvantaged neighbourhood or attended an under-performing school.
Employers should also ensure that all internships are advertised publicly and recruited on merit, not based on networks or who an individual knows, and be aware of the impact of recruiting workers from a narrow pool of universities.
"The Government should ban unpaid internships," the report says, adding: "Employers need to review their work experience policies to ensure access is fair and transparent, ensuring that all posts are publicly advertised to allow a more diverse range of candidates to apply."
Research published in 2014 found that 31% of university graduates working as interns were doing so for no pay. It suggested that many less advantaged young people cannot afford to work unpaid, and were therefore missing out on opportunities that would help them secure a paying job.
The cross-party group of MPs and peers also notes that some employers told them that they simply do not receive job applications from good candidates from poorer backgrounds.
"Employers look for confidence, resilience, social skills and self-motivation in their employees, but for those who have had little to no exposure to extracurricular activities, work experience or mentoring, these skills can be difficult to acquire," the report notes.
"A clear message from our evidence sessions was that we need to become better at inspiring our youngsters to reach their full potential, especially for those who start out at a disadvantage."
APPG chair, Justin Madders MP, said: "If the current government is serious about improving access to top jobs for those from less advantaged homes, they need to take a much more strategic approach.
"This means linking the work of schools, universities and employers to build a real business case and practical plan for improving social mobility."
Alan Milburn, chair of the Social Mobility Commission, said: "Research has consistently shown that people from more affluent backgrounds, who attend private schools and elite universities, take a disproportionate number of the best jobs while those from poorer backgrounds are being systematically locked out.
"Many top firms are doing excellent work in opening their doors to people from all social backgrounds, but there are still too many that need to wake up and realise that it makes sound business sense to recruit people from all backgrounds."
A Department for Business, Energy and Industrial Strategy spokeswoman said: "The Government is committed to building an economy that works for all, not just the privileged few.
"That's why we have agreed with (RSA chief executive) Matthew Taylor that his review on modern working practices will also look at the issue of unpaid internships."