The EU warned African and other countries on Wednesday that their citizens will find it harder to get visas to Europe if they refuse to readmit economic migrants under the bloc's efforts to curb migration.
Brussels has been seeking greater cooperation from such countries to take back irregular migrants since Europe was hit in 2015 with its worst migration crisis since World War II.
"I cannot understand how a country can refuse to take back its nationals" when they have entered Europe illegally, EU migration commissioner Dimitris Avramopoulos told a press conference in Brussels.
"We will introduce stricter conditions for processing visas when a partner country does not cooperate sufficiently on the readmission of irregular migrants," Avramopoulos added.
Under international law, European countries do not have to admit migrants seeking jobs but are required to take in those people fleeing war and persecution.
EU officials say the vast majority of people from sub-Saharan Africa are economic migrants and they have stepped up efforts to return them to their home countries.
But EU sources and analysts said African countries have dragged their feet on readmitting them, mainly because the money they send home from abroad boosts their economies.
"Countries like Mali, Senegal or Ivory Coast cooperate very little," a diplomat told AFP.
"We must fight to obtain the famous consular pass (to return a migrant to his country) and that undermines the ties of trust we must have with these countries."
Under the proposal, if the commission and member countries find other countries are uncooperative on returns, they can toughen rules on granting visas.
These include the processing time of applications, the length of validity of visas issued, the cost of visa fees and the exemption of such fees for certain travellers such as diplomats.
The commission, the EU executive, said 14 million tourist and business visas for short stays, up to 90 days maximum every six months, were granted in 2016.
These visas are required for citizens of around 100 countries and allow them to travel freely in 26 European countries in the so-called Schengen zone.