Members of the House of Lords said on Friday they would try to attach conditions to legislation giving Prime Minister Theresa May the power to trigger the country's exit from the European Union.
On Wednesday, May won approval from parliament's lower chamber for the legislation. The upper chamber, the House of Lords, is due to begin debating the bill on Febuary 20.
The fact the bill passed through the House of Commons without amendment has raised expectations it will enjoy an equally smooth passage in the unelected House of Lords, where May's Conservatives do not have a majority.
One amendment put forward by opposition party the Lib Dems, calling for a second referendum on the final Brexit deal, has the backing of House of Lords members from both the main opposition Labour Party and May's Conservatives.
"The Liberal Democrats will fight to ensure that the Brexit Bill does not get rubber-stamped through the House of Lords. It is our job to scrutinise legislation and we will not be silenced in the Lords," Dick Newby, Lib Dem leader in the Lords said in a statement.
The Lib Dems have also put forward a second amendment which would require the government to guarantee the rights of EU citizens resident in Britain and British citizens living elsewhere in the EU.
Other amendments proposed by peers from Labour and Welsh party Plaid Cymru include those requiring a commitment from the government to seek to retain membership of the EU's single market and to give parliament approval of the final Brexit deal.
Peers are also seeking to require the government to give parliament regular updates on negotiations and to maintain an open border between the Irish republic and Northern Ireland.