Bath have been fined £60,000 for allowing Taulupe Faletau to feature in Wales' autumn international clash with South Africa.
Wales' fourth autumn Test fell outside World Rugby's official release window, but Bath released Faletau for the 24-22 victory in Cardiff on December 2.
Bath admitted breaching Premiership Rugby regulations, and an initial £90,000 fine was reduced by £30,000.
Premiership Rugby defended their policy of enforcing sanctions for clubs flouting the rulings, in confirming Bath's acceptance of punishment.
"This board policy has been an essential one, especially as there has been an increasing number of international matches being organised outside the specified international weeks," said a Premiership Rugby spokesman.
"The agreed policy is well known to clubs, players and unions."
Bath have duly become the second Premiership club to fall foul of releasing players outside of World Rugby's agreed autumn Test window.
Northampton Saints were sanctioned in 2013 for releasing George North to feature for Wales.
"Bath Rugby have today been fined £60,000 after admitting breaching Premiership Rugby Board policies," read a Premiership Rugby statement.
"The sanction was imposed under an independent process managed by Sport Resolutions.
"It relates to the Premiership Rugby Board policy around international duty and specifically Taulupe Faletau being released for a fourth international outside the periods specified in World Rugby Regulation 9.
"The policy is only to release non-England players for Tests matches in accordance with the requirements of World Rugby Regulation 9.
"Bath Rugby's full co-operation with the process was acknowledged and, in mitigation, it was decided to reduce the initial £90,000 sanction to £60,000, a figure that covers the 2017-18 and 2018-19 seasons."