This paper proposes a model of a legislature, formed by several parties, which have to vote for or against a certain bill in the presence of a lobbyist who is interested in a certain outcome of the vote. We show that the ease of manipulating a legislature decision by the lobbyist is increasing with the number of parties. A high threshold leads to fewer parties represented, and consequently, decreases the ease of changing a legislature decision by the lobbyist. On the other hand, a high threshold may cause a misrepresentation of voters. We show that if the threshold is higher that 6%, the impact of the misrepresentation effect becomes significant.