Alpha Group International PLC (AIM:ALPH) shares climbed 5% after it confirmed that it has received a "preliminary and conditional" cash takeover bid from NYSE-listed Corpay.
The UK provider of financial solutions to corporates and institutions, formerly known as Alpha FX, said its board had unanimously rejected the proposal after careful consideration.
Under London's 'put up or shut up' rules, Corpay has until 5pm on 30 May to either make a firm offer or back off.
Alpha said it will make a further announcement "if and when appropriate".