Three of South Korea's opposition parties have submitted a joint request for a parliamentary probe into alleged employment favors at Seoul Metro.

The floor leaders of the Liberty Korea Party, Bareunmirae Party and the Party for Democracy and Peace held a joint news conference Monday where they called for a thorough probe to defuse speculation.

They said irregularities in hires and hereditary succession of employment are a social crime that undermines fairness and trust.

They said similar allegations were also raised at other public firms, including the Korea Land and Geospatial Informatrix Corporation and Incheon International Airport Corporation.

The opposition parties said employees could have abused government policies and a parliamentary investigation must be held to prevent such abusive practices.

The Liberty Korea Party floor leader said the ruling Democratic Party's stance to wait for probe results from the Board of Audit and Inspection is a tactic to waste time and avoid the situation.

The Bareunmirae Party's floor leader said the Board of Audit will do its job while the National Assembly should also play its part as well.

Suspicions of nepotism have been raised at Seoul Metro, which is run by the city government, involving alleged employment favors given to relatives of current and former employees.