(Adds details of measures under discussion)

BRUSSELS, July 11 (Reuters) - Euro zone finance ministers were pressing Greece to commit to a number of additional budget and reform measures on Saturday before they would consider opening negotiations on a bailout, sources close to the talks said.

At a crisis meeting of the Eurogroup in Brussels, ministers were trying to draft a joint statement that would list actions Athens should take beyond those proposed by Prime Minister Alexis Tsipras in his request for a three-year loan.

With European Union leaders due to meet on Sunday, seeking to prevent a Greek bankruptcy causing Athens to drop out of the euro, ministers want Tsipras to both do more to improve state finances and also take immediate legislative steps to give them better assurance Greece would not renege on promises as it has before.

Among the additional measures cited by several sources were commitments to more rigorous reforms of labour market practices, including collective bargaining, more ambitious pension changes and reforms to product markets that restrict competition.

Some ministers were pressing for Greece to legislate as early as Monday on proposed changes to value added tax.

(Reporting by Francesco Guarascio and Renee Maltezou; Editing by Alastair Macdonald and Jonathan Oatis)