At a recent game of duplicate, my LHO opened 1C, this was not alerted, but later we were told by the oposition that it is possible to open 1C with only 3 cards and at least opening points (in the case in question there were 15 points).
I have tried to find a ruling on this and there seems to be some contradiction in the rules.
According to the Orange Book......1C shows 3 + cards, which I take to mean a minimum of 4 cards....as shown here:-
5 G 3 Players should not alert:
(a) The calls specified in 5 C and 5 D as announceable.
(b) Calls above 3NT unless specified in 5 E 4 (a) to (c).
(c) Opening bids:
(1) 1♣ or 1♦ showing three plus cards, not forcing, which are considered natural.
But according to the 'Announcing and Alerting Summary'......shown here...http://www.ebu.co.uk/publications/ConventionCards-SystemsInformation/Announcements%20Table.pdf
no action needs to be taken with 3 cards.
DAK which of these is correct.