VIENNA (Reuters) - An Austrian opposition lawmaker said on Thursday five Austrian citizens who made critical comments about Turkish President Tayyip Erdogan had been held at Turkish airports and deported.

FILE PHOTO: A portrait of Turkey's President Tayyip Erdogan is seen as supporters wave flags before his speech at the Ethias Arena in Hasselt, Belgium, May 10, 2015. REUTERS/Francois Lenoir/File Photo

Peter Pilz, from the Austrian Greens, is already leading a campaign against what he calls Erdogan’s spy network in Europe operating via religious attaches in Turkish embassies and mosque groups who he says monitor Erdogan critics and report on them.

Turkey’s foreign ministry has previously rejected Pilz’s allegations, but was not immediately available for comment on Thursday.

An Austrian Foreign Ministry spokesman said that three Austrian citizens wanting to return to Austria from Turkey are currently being prevented from leaving Turkey on the grounds they might have violated Turkish law.

“This obviously has a political background,” the spokesman said, adding Austria was in contact with the three people and working towards their return to Austria.

Austrian and German authorities are investigating the allegations that Turkey is using religious groups to spy on Erdogan’s opponents in Europe.

Pilz said he had documented five cases of people holding Austrian citizenship who were detained in Turkey. In one case an official in Turkey told the man there had been complaints against his criticism of Erdogan from Austria.

In a second case, an Austrian citizen was confronted at the airport with a text message critical of Erdogan on his phone.

In another case a Turkish official at the consulate in Vienna told the man, who admits he was critical of Erdogan, that Turkey’s interior ministry had initiated his travel ban. These five Austrians were held between one and three days in Turkey.

“If you have made critical statements about Erdogan in Austria, I recommend that you don’t go to Turkey,” Pilz told a news conference sitting next to two men who had been detained.

The German government said on Wednesday there had been a significant increase in Turkish spying in Germany, where tensions within the large Turkish community have escalated ahead of next month’s referendum on Turkey’s presidency.

Erdogan has accused West European countries of failing to condemn a July putsch against him quickly or strongly enough.

West European countries have expressed concern about his crackdown on journalists, judiciary, academics and others, often under the suspicion they supported Erdogan’s foe, U.S.-based cleric Fethullah Gulen.