Culture secretary Jeremy Hunt is to be investigated over allegations he failed to register donations from media companies including BSkyB.
The office of the parliamentary standards commissioner, John Lyons, confirmed on Monday that it had launched an inquiry following a complaint from Labour MP Steve McCabe.
Hunt is accused of failing to declare his attendance at eight events between July 2009 and March 2010 hosted by media companies and estimated to have cost £27,000.
The networking events took place when the Conservatives were in opposition and the then shadow culture minister Ed Vaizy declared his and his boss' attendance - however Hunt himself did not.
Hunt has claimed he only attended three of the meetings and has said he will amend the register of MPs interests to reflect this.
The investigation comes amid calls from Labour for Hunt to resign over his handling of News Corporation's bid to take over BSkyB in 2010.
Hunt's special adviser, Adam Smith, was forced to resign after falling on his sword and admitting he shared more information with News Corp than he should have done during the bidding process. He is due to appear before the Leveson inquiry on Friday.
The Labour Party has accused Hunt of acting inappropriately as News Corp's "cheerleader" inside the government.
The culture secretary has said he will respond to the allegations when he gives his evidence to the Leveson inquiry later this month.
"He is confident that his evidence will vindicate the position that he has behaved with integrity on every issue," a spokesman for Hunt said.