Shares in Thomas Cook closed down 4.85 per cent to 125.5p per share this afternoon while TUI's share price was 2.55 per cent lower at 14.34p per share.
Last night's "no" vote will prolong uncertainty that currently surrounds the situation in Greece as officials try to strike a mutually acceptable deal with its troika of creditors.
Greek authorities closed the country's banks ahead of yesterday's referendum, which are yet to re-open, and imposed capital controls. Consequently there's a €60 (£38) daily limit on ATM transactions in the country.
However, tourists are exempt from this as long as they use credit and debit cards issued outside of Greece.
Read more: Should UK tourists take cash to Greece?
This comes after shares in the travel firms fell after the Tunisia beach the terrorist attacks in Tunisia which left more than 30 dead, many of them British tourists.