BRUSSELS (AP) — The head of the European Union’s border and coast guard agency faces a grilling Tuesday by EU lawmakers as pressure mounts over allegations that Frontex was involved in illegal pushbacks aimed at preventing migrants or refugees entering Europe through the Greek islands.

A joint investigation published in October by media outlets Bellingcat, Lighthouse Reports, Der Spiegel, ARD and TV Asahi said that video and other publicly available data suggest Frontex “assets were actively involved in one pushback incident at the Greek-Turkish maritime border in the Aegean Sea.”

The report said personnel from the agency, which monitors and polices migrant movements around Europe’s borders, were present at another incident and “have been in the vicinity of four more since March.”

Frontex announced an internal investigation, and Executive Director Fabrice Leggeri said in October that “so far, no documents or other materials have been found to substantiate any accusations of violations of the law or the Frontex Code of Conduct by deployed officers.”

He said the agency does “not tolerate any violations of the fundamental rights in any of our activities.”

Pushbacks are considered contrary to international refugee protection agreements, which say people should not be expelled or returned a country where their life and safety might be in danger due to their race, religion, nationality or being members of a social or political group.

Frontex’s board met to discuss the allegations late last month. The board said afterwards that the European Commission had ordered it to “hold a further extraordinary meeting within the next two weeks in order to consider in more detail the replies provided by the agency.”

The allegations are extremely embarrassing for the Commission. In September it unveiled sweeping new reforms to the EU’s asylum system, which proved dismally inadequate when over 1 million migrants arrived in 2015, many of them Syrian refugees entering the Greek islands via Turkey.

Part of the EU's migration reforms includes a system of independent monitoring involving rights experts to ensure that there are no pushbacks at Europe’s borders.

Frontex says its work in the eastern Aegean Sea has been complicated by a dispute between Turkey and Greece over their maritime borders. Greek and Turkish coast guard ships are routinely involved in standoffs and threats in the relatively narrow stretch of water that separates the two countries.