Nautilus International is urging its members to get in contact with any concerns following the outbreak of war between Russia and Ukraine.
The Union's officials across its branches in the United Kingdom, the Netherlands and in Switzerland are working with governments and international partners to ensure members' safety.
Crew changes are expected to be disrupted following the closure of all commercial flights to Ukraine on Thursday. Supply of ships' crew could also be hit as seafarers are called up to defend their country.
The Union has been made aware that payment problems may arise for some crew. A news report from Lloyd's List suggested that the fear of sanctions might stop some employers paying salaries into Russian or Ukrainian bank accounts.
Lloyd's Joint War Committee last week designated Ukranian and Russian waters in the Black Sea and Sea of Azov as listed areas.
An emergency meeting of The Warlike Operations Area Committee (WOAC) was held in London on Thursday.
In a statement WOAC said: 'Representatives met today in response to this morning's sudden and unacceptable invasion of the Ukraine by Russian forces to consider the threat posed to UK seafarers, and seafarers generally of all nationalities in the region. They noted their particular concern for all seafarers wherever they are serving at sea at this deeply worrying time.'
'The WOAC proposes a Warlike Operations Area be declared with immediate effect for all Ukrainian, Russian and International Waters north of 44°North in the Black Sea.'
The WOAC consists of Nautilus International, the RMT union and the UK Chamber of Shipping.
Ship traffic in and out of the Sea of Asov appeared to have been blockaded on Thursday with reports of missile strikes and explosions in the key ports of Odessa and Mariupol, according to Lloyd's List.
Operations at Ukraine's ports were suspended by the country's military on Thursday, according to Reuters news reports.
Members can access assistance 24 hours a day 7 days per week via the Nautilus24/7 emergency helpline: