A federal labour agency has accused the Washington Post on Thursday of repeatedly violating labour laws by failing to negotiate with the newspaper's union over extra work employees performed for its radio station.

The National Labor Relations Board said the Post has violated the laws since the beginning of 2006, when it failed to negotiate with the Washington-Baltimore Newspaper Guild, which represents more than 1,200 employees.

The complaint also states employees were not fairly paid for work they contributed to Washington Post Radio, and the newspaper did not properly negotiate with the union before requiring employees do extra work for The Onion, an independent fake newspaper the Post prints, according to a statement by the labour board.

The newspaper is scheduled to appear before an administrative law judge in September.