The electoral watchdog said those switching camps were clearly driven by positions and personal gains.
Furthermore, it added the move could also be perceived as an escape route from criminal prosecution.
In a statement this afternoon, Bersih's steering committee expressed grave concern over the possible crossover of Umno lawmakers to Bersatu.
“Such an act by MPs is a betrayal to the mandate given by the voters in the 14th general election who voted them into parliament based on the platform of the political party they contested.
“It also makes a mockery of our democracy if MPs of losing parties such as Umno can easily cross over to the ruling parties and enjoy all the glory and benefits of being in the government instead of playing their role as opposition to provide checks and balances in a democracy,” it added.
Bersih also questioned if Umno lawmakers who joined Bersatu would be held accountable for their past abuses of power and corruption under the previous regime?
The watchdog also noted the suggestion for the government to legislate an anti-hopping law.
“Nevertheless, an anti-hopping law has been ruled as in violation of the right to freedom of association guaranteed under Article 10 of the Federal Constitution by Federal Court in the case involving Kelantan state assembly and Nordin Salleh in 1992,” it added.
Bersih said the issue of an en-masse cross over highlighted an institutional contradiction in the system that required careful deliberation for a solution.
“On one hand, lawmakers must have the adequate freedom to even go against party line for parliamentary debates to be meaningful.
“On the other, the en masse crossover of lawmakers is harmful to democracy as it can both substantially alter election outcome and cause instability by triggering inter-party competition in courting defections,” it added.
In view of this, Bersih reiterated its call for extensive debates on the electoral system and party system in the agenda of electoral reform.