There seem to be many different uses of 'call' in different card games.
The Laws and Practice of Whist (Caelebs, 1859) says:
Calling is the only positive avowal permitted at whist. It is an intimation to partner to lead trumps: hence, with a powerful hand it is not advisable to call, lest you put the adversaries on their guard; neither is it advisable, unless partner has the lead, to call before the latest period allowed, viz.: before your own turn to play.
So calling here is a particular signal to your partner (not a verbal call, but a signal encoded by the choice of cards played). But it also seems to be used in the sense of 'calling the game', when you reach a point where you have sufficient strength to win regardless of your opponents' actions.
The Compleat Gamester (Richard Seymour and Charles Johnson, 1754) under 'Whist' has
If either side are at 8 groats, he hath a Benefit of calling, Can ye? If he hath 2 Honours in his Hand and the other answers 1, the Game is up, which is 10 in all; but if he hath more than 2 he shews them, which is the same Thing; but if he forgets to call, after playing a Trick, he loseth the Advantage of calling for that Deal.
I believe this is current usage in other trick-taking games like bridge - if at the end you have the right number of trumps (say) then you can declare victory without actually playing out the rest of the game.
The 'call' of poker might be similar to this older usage. OED has
When the bet goes round to the last player ... and he does not wish to go better, he may simply ‘see it’ and ‘call’.
quoting Longman's Magazine from September 1883. The sense is that it is now time to see who has won (and by matching the amount bet, the person who says 'call' is still in the game).
Best Answer
Some say that they're keeping their lips zipped where I'm from, but its more associated with secrets... But it can work. "He kept his lips sealed when he knew he ought to say something about... his manager?" What's the context? Either way, there's probably more creative ones. Clammed up is one...
Coming at the question at another angle, I don't think there's a popular metaphor mainly because the good ones are associated more with bondage and the like. Gagged, muzzled... Yeah, those can work but have a really ugly connotation, and I can't think of anything else that fits in the set.