The GBTA, alongside its European partner organisations, is urging a coordinated approach to the validity period of the European Digital Covid Certificate (DCC).
In a joint statement to the European Union and its member states, the organisations urge countries to come together around the 270-day validity for certificates.
The statement says some member states continue to implement their own rules which causes confusion for travellers.
Suzanne Neufang, CEO GBTA, said: "Ensuring the harmonisation of measures such as the validity period of the DCC across the Member States will be crucial to the recovery of the European and global travel industry as well as to the economy as a whole.
"The successive lockdowns we experienced in Europe and around the world in 2020 dealt a blow to the global business travel industry, which suffered a 52 per cent decline in business travel and €662 billion in lost business travel spend; a coordinated and harmonised approach to the DCC is needed to support the return to travel and the recovery of the business travel industry."
A similar call was made by aviation organisations earlier this month who urged EU governments to lift all travel restrictions for fully vaccinated travellers, as the new EU-wide travel regime was implemented.
ACI Europe (Airports Council International) and the International Air Transport Association (IATA) said those holding a valid Covid-19 vaccination certificate should not face any restrictions when travelling within the EU.