diff --git a/lib/payrix/request_options/search.rb b/lib/payrix/request_options/search.rb
index 72e0bea..a20c5b8 100644
--- a/lib/payrix/request_options/search.rb
+++ b/lib/payrix/request_options/search.rb
@@ -3,6 +3,7 @@
 require 'payrix/request_options/search/node'
 require 'payrix/request_options/search/atom'
 require 'payrix/request_options/search/equals'
+require 'payrix/request_options/search/in'
 require 'payrix/request_options/search/greater'
 require 'payrix/request_options/search/less'
 require 'payrix/request_options/search/compound'
@@ -33,6 +34,10 @@ def self.equals(field, value)
         Equals.new(field, value)
       end
 
+      def self.in(field, value)
+        In.new(field, value)
+      end
+
       def self.greater(field, value)
         Greater.new(field, value)
       end
diff --git a/lib/payrix/request_options/search/in.rb b/lib/payrix/request_options/search/in.rb
new file mode 100644
index 0000000..c4c2dc9
--- /dev/null
+++ b/lib/payrix/request_options/search/in.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Payrix
+  module RequestOptions
+    module Search
+      # A builder class that constructs a valid 'equals' search filter.
+      class In < Atom
+        def initialize(field, value)
+          value = "''" if ['', nil].include?(value)
+
+          super(field, :in, value.to_s)
+        end
+      end
+    end
+  end
+end