The Scottish Premier League announced the club have "not paid a number of bonuses and appearance payments" and face a disciplinary hearing, with a full range of sanctions at the SPL's disposal.
Hearts insisted bonus payments from the William Hill Scottish Cup final win over Hibernian on May 19 had been paid. However, it is understood bonuses had not been received last week, so the payments were likely included in this month's pay packet on December 16, six months late. Payments of bonuses due this season are understood to be in arrears, amounting to a six-figure sum.
A statement from the SPL read: "As a result, and as described in SPL Rule A6.23, Heart of Midlothian is subject to an embargo on the registration of players until such time as the SPL board is satisfied the remuneration default no longer continues."
Hearts acknowledged the SPL's statement and are taking legal advice.
The club were initially placed under a 60-day transfer embargo on October 24 for failing to pay their players and some staff on time for two months. That sanction was due to end on Sunday.
Hearts had some positive news for supporters yesterday when they announced their share issue, which closed on Wednesday, had raised more than £1m. This is short of the £1.79m target but a further £161,000 has been taken thanks to increased attendances for games against St Mirren, Celtic and Aberdeen.
More than 4000 supporters have backed the initiative although Hearts concede they are still £800,000 short of plugging a £2m shortfall and have pleaded with fans to purchase half-season passes and tickets for the remaining 10 home games. Next month's Scottish Communities League Cup semi-final with Inverness Caledonian Thistle at Easter Road also provides a chance for the club to raise vital income.
Director Sergejus Fedotovas, said: "There is still significant work to be done but this time there is a tangible focus that involves fans getting back to what they do best: supporting the team at Tynecastle in great numbers."