Federal police officers control the passenger data during the presentation of the new automated border control system EasyPASS at Frankfurt International Airport | Alex Grimm/Getty Images Tighter security checks could cause longer waits on Schengen borders Authorities will toughen up exit as well as entry controls.

Worry about homegrown terrorists is prompting tighter controls starting Friday at airports, seaports and border crossings for those who enter or exit the 26-country Schengen passport-free area.

Following an amendment to the Schengen Border Code approved last month, border officers now have to check the documents of all travelers against databases like the Schengen Information System, Interpol and registers of wanted persons.

Previously, EU citizens leaving the zone were generally only checked for the expiration date of their passports and if the passport photo matched the traveler. For travelers from non-EU countries, systematic checks against the databases were already compulsory, but only when entering, not exiting the Schengen area.

The new policy doesn't impose extra checks on people traveling within the zone.

The regulation is a response to "the increase of terrorist threats," the European Council explained in December.

The regulation is a response to "the increase of terrorist threats," the European Council explained in December. According Europol, an estimated 5,000 EU citizens traveled to conflict zones like Iraq and Syria between 2013 and 2015 and joined terrorist groups like ISIS. Back in Europe, some then became involved in terrorist attacks.

Member countries wanted tighter checks as far back as the beginning of 2015, but the Commission and Parliament initially opposed the idea, worrying it could lead to a reimposition of internal borders within the zone.

Prepare for delays

The Belgian federal police warned that the reinforced security measures could cause delays and advised travelers to prepare and come early to the checkpoints. People who haven't updated their addresses or have other issues with the police should "pay a visit to a police station before leaving," a police spokesman said.

To avoid long queues at land and sea borders, the regulation allows the authorities to carry out "targeted" checks against databases, if there is an assessment showing that this does not pose a risk to internal security.

Airports with "infrastructural difficulties" preventing systematic checks are allowed to check on a random basis as well, but only for a transition period of up to 18 months.

"This is a small change in regulation, but it has a strong effect on us," because more people will have to be checked, said a police spokesperson at Frankfurt airport, Germany's largest. The airport hopes to make greater use of the EasyPASS system, an automatic identity checking system.

Passengers traveling by train to the U.K. will not be "adversely" affected, a Eurotunnel spokesperson said.

The Belgian and Dutch border police have run tests to limit waiting times. Robert O'Meara from the Airports Council International, a lobby group, said Schengen members are obliged "to ensure that border control resources are boosted accordingly."

Passengers traveling by train to the U.K. will not be "adversely" affected, a Eurotunnel spokesperson said, because they already undergo passport checks since the U.K. is not part of Schengen.

Ireland, Bulgaria, Croatia, Cyprus and Romania are EU members that also are not part of the Schengen area, while Switzerland, Norway, Liechtenstein and Iceland are not part of the EU but are in Schengen.