Q:

Can a Kantian bluff in poker?

Kantians aren't allowed to lie---if it were a universal law of nature that everyone lied all the time, no communication would be possible at all, no words would have meaning, and lying itself would become impossible.
Poker is a game that involves a lot of lying. Or if not lying, something very much like lying: systematic attempts to mislead people, aka bluffing. (Actually I don't think this is supposed to be much of the game for pros. When you get really good it's just about statistics.) But since everyone knows we are going to lie in poker the situation seems to be somewhat different than in normal communication.
Does this make a difference? Can a Kantian bluff in poker?

A:

Bluff - lying - in poker is a case of what Onora O'Neill terms selective falsehood. Let her explain this idea before I go further : 

Another alluring, but on reflection impossible, maxim of communication to which Kant turned his attention (in a form few of his admirers find adequate) is that of falsehood. ... [I]t appears that a maxim of falsehood in communication could not serve as a universal principle of communications among a plurality of rational beings, or beings who are becoming rational. For if falsehood became the maxim of "communications" among such beings, comprehension itself would cease, and so also the possibility of communication. This is not to say that a maxim of selective falsehood would be an impossible one for regulating the communicating of a plurality of partially free and rational beings. Plenty of actual communities get on well with a universally shared convention of falsehood in response to intimate inquiries or about punctuality or in relations with strangers. But the very possibility of recognizing what is said in such contexts as falsehood presupposes comprehensibility, and thus also that standards of truth-telling obtain more generally in such communities.' (O. O'Neill, Constructions of Reason : Explorations of Kant's Practical Philosophy, Cambridge : CUP, 1989, 45.)

The main point is that what is up for universalisation in your question is not lying simpliciter but a mutually voluntary activity (the game of poker) in which people agree for purposes of gain or entertainment to engage in a competition with specific other persons in which they and the others know that lying (within limits) is allowed. This is selective lying. 
There is no reason why the maxim, 'agree for purposes of gain or entertainment to engage in a competition with specific other persons in which they and the others know that lying (within limits) is allowed', cannot be universalised - that it involves a contradiction in conception or a contradiction in the will. 
But the reply may come : Kant rules out lying and you cannot get around this by contextualising lying. Why not ? Two points : first in the Groundwork the prohibition on lying precisely is contextualised : it is contextualised to making a lying promise to repay a debt (§§ 18-19). While the maxim behind this cannot be universalised, the maxim behind my poker case can be. 
And in 'On a Supposed Right to Lie from Philanthropy' Kant says :

Truthfulness in statements that one cannot
   avoid is a human being's duty to everyone, however great the disadvantage to him or to another that may result from it ... (SRL 8:426). (McGregor Cambridge tr.)

The immediate context is the supposed right to lie to the murderer at the door. But lying in poker is hardly a violation of 'Truthfulness in statements that one cannot avoid'. It is, and is recognized as, selective lying. 
The second point is that we need to draw a distinction between what Kant thought the universalisation constraint implies in particular cases or types of case, and what it actually does imply. Even if Kant had pronounced against bluff in poker, it would not follow that the universalisation constraint cannot, as I have argued above, consistently allow it. 

A:

Can a Kantian bluff in poker?

What an interesting question. I do not believe that bluffing in poker is the same as lying in daily life for the same reason that acting in theater is not lying. The players and actors agree to follow a specialized set of rules that apply to a single activity which is outside the collection of transactions that people encounter every day.
Other writers have arrived at a similar conclusion. Perverse Egalitarianism, "Running The Red Light, Being Late For A Poker Game", April 5, 2009. The article is here; https://pervegalit.wordpress.com/2009/04/05/running-the-read-light-being-late-for-a-poker-game/

