Montenegro's Foreign Ministry said the Serbian ambassador was called to explain "worrying and inappropriate" language used by Serbian church and government officials after Montenegro's government drafted the law earlier this month.
The draft bill calls for all religious communities in the country to provide proof that they owned their property before 1918, when Montenegro lost its independence and became part of the Serb-dominated Kingdom of Serbs, Croats and Slovenes. If they don't, the property becomes state-owned.
Serbia says the measure will result in the forced takeover of Serb Orthodox Churches and monasteries on Montenegro's territory. Montenegro, which split from much larger Serbia in 2006, denies the claims.
The row escalated Wednesday as Serbian government minister Nenad Popovic branded Montenegro a "hostile" and "criminal" state, urging a "fierce" response by Serbia if the law is adopted by Montenegro's parliament.