Barclays may be facing a second fine in connection to its June 2012 settlement with US authorities over the alleged rigging of the main interbank lending rate, known as the London Interbank Offered Rate or LIBOR.The size of the fine is not clear but as of a few weeks ago was calculated to stand at around $60m, according to a source cited by Bloomberg.US prosecutors will not ask Barclays to plead guilty but do believe it has breached its three-year old settlement. UBS on the other hand is expected to be prosecuted for the repeated breach of that settlement, as reported by The Wall Street Journal on Thursday night.The latest penalty will come on top of another fine which the US Department of Justice is expected to announce in coming days, resulting from the probe into five banks' roles in the alleged manipulation of foreign exchange markets.Among the institutions whose activities were being probed besides Barclays, are Citigroup, JP Morgan Chase, RBS and UBS.