The BBC's Oana Lungescu in Ljubljana says they are expected to issue a joint warning to Tehran that more sanctions against Iran's banks are being readied.
They are pressuring Iran to abandon its nuclear programme, rejecting claims it is solely for peaceful purposes.
There will be a tough joint message to Tehran about further sanctions against Iranian banks linked to nuclear proliferation and terrorism, our correspondent says.
Mr Bush is also expected to apply pressure on individual European businesses to take a harder line.
Barclays Bank, based in Britain, has already responded to US pressure, and ended all dealings with Iran's Saderat Bank and Bank Melli.
The warning of sanctions is a stick that Washington is keen to wield, but it is ready to give the carrot one more try, our correspondent says.
EU foreign policy chief Javier Solana will go to Iran at the weekend with an upgraded offer of economic and political incentives.
The UN Security Council has approved three rounds of sanctions against Iran.
These include asset restrictions and travel bans on Iranian individuals and companies said to be involved in nuclear work.
The sanctions also ban the sale to Iran of so-called dual-use items - items which can have either a military or civilian purpose.