MapLike.DefaultValuesIterable is not serializable

Hi guys,
I have mutable Map (scala.collection.mutable.LinkedHashMap actually). It is populated with key-values pairs ant then its values collection (scala.collection.Iterable) is converted to java.util.Collection and set into legacy Java object:

lazy val taxMap: Map[A, B] = new LinkedHashMap[A, B]...populateTaxMap(taxMap)...postingDTO.setAmounts(taxMap.values.asJavaCollection)

The problem is that when this legacy DTO object is sent to another service via network, NotSerializableException is thrown:
java.io.NotSerializableException: scala.collection.MapLike$DefaultValuesIterable is not serializable

Could you please advise what the reason of this problem is?
Thanks,Vladimir