More than 9,000 U.K. employers have until Wednesday midnight GMT to provide reports on the pay imbalance between their male and female workers.

As of Tuesday morning, 8,874 employers had filed their figures to the U.K. gender pay gap service. 

Based on the law, all employers in the U.K. with 250 or more employers must calculate their mean gender pay gap, their median gender pay gap, their mean bonus gender pay gap, their median bonus gender pay gap, the proportion of men and women in the organization receiving a bonus payment, and the proportion of men and women in each quartile pay level. 

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"Shining a light on where women are being held back means employers can begin to take action," a U.K.  Home Office spokesperson said. "Reporting gender pay gap data is not optional, it is the law."

Some of the biggest offenders were airlines Ryanair (RYAAY) - Get Report , EasyJet (ESYJY) and Virgin Atlantic, banks HSBC (HBCYF) , Goldman Sachs (GS) - Get Report and JPMorgan (JPM) - Get Report .  The latter two are holdings in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio.