Let X be a set of reals and Cp(X) be the set of all continuous real-valued functions on X with the pointwise convergence topology. By the result of Gerlits and Nagy the space Cp(X) has the Frechet-Urysohn property (a generalization of first-countability) if and only if the set X is a gamma-set (i.e., has a combinatorial covering property). The existence of uncountable gamma-sets of reals is independent of ZFC. Tsaban proved that sets with some special combinatorial structure are gamma-sets. We generalize this class of sets and prove that their products have the property gamma. We also show that for every set X from our class and every gamma set Y, the product space X x Y have a strong property weaker than gamma. These investigations are motivated by the result of Miller, Tsaban and Zdomskyy that under CH, there are two gamma-sets whose product space is not even Menger (in particular it is not gamma). This is a joint work with Magdalena Włudecka.