[What exactly is sui juris? Doesnt the Pope still have some authority in the UGC? Thanks! ]
Depends on who you talk to within the papal Catholic structure.
Unless things have changed and I am unaware of it, being 'In Communion With Rome' also means accepting Papal authority. Although if you read some of the posts from those who accept the Unia, you will get various opinions on just what it means.
According to the American heritage Dictionary sui juris means -
SYLLABICATION: sui ju-+ris
ADJECTIVE: Law Capable of managing one's own affairs.
ETYMOLOGY: Latin su iris : su, of one's own + iris, genitive of is, right, law.
From the Roman Catholic New Advent Encylopedia -
Sui iuris is a Latin phrase that literally means “of one’s own right”. It is usually spelled "sui juris" in civil law, which uses the phrase to indicate legal competence, the capacity to manage one’s own affairs (Black's Law Dictionary, Oxford English Dictionary). The English word “autonomous” is derived from the Greek words that correspond to Latin "sui iuris".
Roman Catholic ecclesiastical use
Church documents such as the Code of Canons of the Eastern Churches apply the Latin term "sui iuris" to the particular Churches or rites that together compose the Roman Catholic Church. By far the largest of these "sui iuris" or autonomous Churches is that known as the Latin Church or the Latin Rite. Over this particular Church the Pope exercises, as well as his papal authority, the authority that in other particular Churches belongs to a Patriarch. He is therefore referred to also as Patriarch of the West (http://www.newadvent.org/cathen/05230a.htm
). The other particular Churches are called Eastern Catholic Churches or Eastern Rites, each of which, if large enough, has its own patriarch or other chief hierarch, with authority over all the bishops of that particular Church or rite.
The same term is applied also to missions that, though lacking enough clergy to be set up as apostolic prefectures, are for various reasons given autonomy, and thus are not part of any diocese, apostolic vicariate or apostolic prefecture. In 2004, there were eleven such missions. Three in the Atlantic: Cayman Islands, Turks and Caicos, and Saint Helena, Ascension and Tristan da Cunha. Two in the Pacific: Funafuti (Tuvalu), and Tokelau. Six in central Asia: Afghanistan, Baku (Azerbaijan), Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan.
What's interesting is the fact that the UOC-MP is considered an automonous Church within the Moscow Patriarchate while the UGCC is considered a sui uris Church within the Roman Patriarchate. As such, each has about the same independence from their recognized mother churches. Yet to our 'Eastern Catholics not In Communion With Orthodoxy' the UOC_MP is subservient to Moscow while they are free and independent from Rome! And they state this as they cry about the Popes failure to grant them a Ukrainian Patriarch!